3 ways to make better decisions -- by thinking like a computer | Tom Griffiths

938,894 views ・ 2018-10-05

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If there's one city in the world
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where it's hard to find a place to buy or rent,
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it's Sydney.
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And if you've tried to find a home here recently,
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you're familiar with the problem.
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Every time you walk into an open house,
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you get some information about what's out there
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and what's on the market,
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but every time you walk out,
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you're running the risk of the very best place passing you by.
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So how do you know when to switch from looking
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to being ready to make an offer?
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This is such a cruel and familiar problem
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that it might come as a surprise that it has a simple solution.
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37 percent.
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(Laughter)
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If you want to maximize the probability that you find the very best place,
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you should look at 37 percent of what's on the market,
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and then make an offer on the next place you see,
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which is better than anything that you've seen so far.
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Or if you're looking for a month, take 37 percent of that time --
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11 days, to set a standard --
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and then you're ready to act.
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We know this because trying to find a place to live
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is an example of an optimal stopping problem.
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A class of problems that has been studied extensively
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by mathematicians and computer scientists.
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I'm a computational cognitive scientist.
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I spend my time trying to understand
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how it is that human minds work,
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from our amazing successes to our dismal failures.
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To do that, I think about the computational structure
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of the problems that arise in everyday life,
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and compare the ideal solutions to those problems
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to the way that we actually behave.
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As a side effect,
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I get to see how applying a little bit of computer science
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can make human decision-making easier.
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I have a personal motivation for this.
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Growing up in Perth as an overly cerebral kid ...
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(Laughter)
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I would always try and act in the way that I thought was rational,
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reasoning through every decision,
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trying to figure out the very best action to take.
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But this is an approach that doesn't scale up
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when you start to run into the sorts of problems
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that arise in adult life.
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At one point, I even tried to break up with my girlfriend
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because trying to take into account her preferences as well as my own
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and then find perfect solutions --
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(Laughter)
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was just leaving me exhausted.
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(Laughter)
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She pointed out that I was taking the wrong approach
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to solving this problem --
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and she later became my wife.
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(Laughter)
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(Applause)
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Whether it's as basic as trying to decide what restaurant to go to
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or as important as trying to decide who to spend the rest of your life with,
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human lives are filled with computational problems
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that are just too hard to solve by applying sheer effort.
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For those problems,
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it's worth consulting the experts:
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computer scientists.
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(Laughter)
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When you're looking for life advice,
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computer scientists probably aren't the first people you think to talk to.
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Living life like a computer --
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stereotypically deterministic, exhaustive and exact --
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doesn't sound like a lot of fun.
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But thinking about the computer science of human decisions
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reveals that in fact, we've got this backwards.
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When applied to the sorts of difficult problems
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that arise in human lives,
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the way that computers actually solve those problems
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looks a lot more like the way that people really act.
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Take the example of trying to decide what restaurant to go to.
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This is a problem that has a particular computational structure.
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You've got a set of options,
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you're going to choose one of those options,
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and you're going to face exactly the same decision tomorrow.
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In that situation,
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you run up against what computer scientists call
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the "explore-exploit trade-off."
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You have to make a decision
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about whether you're going to try something new --
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exploring, gathering some information
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that you might be able to use in the future --
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or whether you're going to go to a place that you already know is pretty good --
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exploiting the information that you've already gathered so far.
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The explore/exploit trade-off shows up any time you have to choose
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between trying something new
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and going with something that you already know is pretty good,
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whether it's listening to music
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or trying to decide who you're going to spend time with.
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It's also the problem that technology companies face
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when they're trying to do something like decide what ad to show on a web page.
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Should they show a new ad and learn something about it,
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or should they show you an ad
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that they already know there's a good chance you're going to click on?
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Over the last 60 years,
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computer scientists have made a lot of progress understanding
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the explore/exploit trade-off,
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and their results offer some surprising insights.
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When you're trying to decide what restaurant to go to,
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the first question you should ask yourself
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is how much longer you're going to be in town.
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If you're just going to be there for a short time,
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then you should exploit.
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There's no point gathering information.
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Just go to a place you already know is good.
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But if you're going to be there for a longer time, explore.
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Try something new, because the information you get
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is something that can improve your choices in the future.
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The value of information increases
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the more opportunities you're going to have to use it.
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This principle can give us insight
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into the structure of a human life as well.
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Babies don't have a reputation for being particularly rational.
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They're always trying new things,
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and you know, trying to stick them in their mouths.
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But in fact, this is exactly what they should be doing.
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They're in the explore phase of their lives,
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and some of those things could turn out to be delicious.
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At the other end of the spectrum,
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the old guy who always goes to the same restaurant
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and always eats the same thing
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isn't boring --
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he's optimal.
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(Laughter)
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He's exploiting the knowledge that he's earned
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through a lifetime's experience.
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More generally,
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knowing about the explore/exploit trade-off
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can make it a little easier for you to sort of relax and go easier on yourself
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when you're trying to make a decision.
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You don't have to go to the best restaurant every night.
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Take a chance, try something new, explore.
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You might learn something.
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And the information that you gain
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is going to be worth more than one pretty good dinner.
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Computer science can also help to make it easier on us
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in other places at home and in the office.
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If you've ever had to tidy up your wardrobe,
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you've run into a particularly agonizing decision:
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you have to decide what things you're going to keep
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and what things you're going to give away.
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Martha Stewart turns out to have thought very hard about this --
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(Laughter)
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and she has some good advice.
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She says, "Ask yourself four questions:
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How long have I had it?
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Does it still function?
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Is it a duplicate of something that I already own?
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And when was the last time I wore it or used it?"
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But there's another group of experts
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who perhaps thought even harder about this problem,
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and they would say one of these questions is more important than the others.
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Those experts?
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The people who design the memory systems of computers.
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Most computers have two kinds of memory systems:
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a fast memory system,
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like a set of memory chips that has limited capacity,
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because those chips are expensive,
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and a slow memory system, which is much larger.
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In order for the computer to operate as efficiently as possible,
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you want to make sure
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that the pieces of information you want to access
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are in the fast memory system,
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so that you can get to them quickly.
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Each time you access a piece of information,
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it's loaded into the fast memory
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and the computer has to decide which item it has to remove from that memory,
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because it has limited capacity.
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Over the years,
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computer scientists have tried a few different strategies
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for deciding what to remove from the fast memory.
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They've tried things like choosing something at random
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or applying what's called the "first-in, first-out principle,"
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which means removing the item
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which has been in the memory for the longest.
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But the strategy that's most effective
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focuses on the items which have been least recently used.
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This says if you're going to decide to remove something from memory,
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you should take out the thing which was last accessed the furthest in the past.
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And there's a certain kind of logic to this.
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If it's been a long time since you last accessed that piece of information,
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it's probably going to be a long time
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before you're going to need to access it again.
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Your wardrobe is just like the computer's memory.
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You have limited capacity,
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and you need to try and get in there the things that you're most likely to need
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so that you can get to them as quickly as possible.
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Recognizing that,
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maybe it's worth applying the least recently used principle
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to organizing your wardrobe as well.
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So if we go back to Martha's four questions,
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the computer scientists would say that of these,
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the last one is the most important.
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This idea of organizing things
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so that the things you are most likely to need are most accessible
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can also be applied in your office.
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The Japanese economist Yukio Noguchi
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actually invented a filing system that has exactly this property.
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He started with a cardboard box,
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and he put his documents into the box from the left-hand side.
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Each time he'd add a document,
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he'd move what was in there along
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and he'd add that document to the left-hand side of the box.
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And each time he accessed a document, he'd take it out,
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consult it and put it back in on the left-hand side.
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As a result, the documents would be ordered from left to right
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by how recently they had been used.
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And he found he could quickly find what he was looking for
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by starting at the left-hand side of the box
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and working his way to the right.
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Before you dash home and implement this filing system --
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(Laughter)
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it's worth recognizing that you probably already have.
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(Laughter)
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That pile of papers on your desk ...
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typically maligned as messy and disorganized,
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a pile of papers is, in fact, perfectly organized --
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(Laughter)
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as long as you, when you take a paper out,
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put it back on the top of the pile,
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then those papers are going to be ordered from top to bottom
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by how recently they were used,
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and you can probably quickly find what you're looking for
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by starting at the top of the pile.
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Organizing your wardrobe or your desk
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are probably not the most pressing problems in your life.
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Sometimes the problems we have to solve are simply very, very hard.
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But even in those cases,
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computer science can offer some strategies
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and perhaps some solace.
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The best algorithms are about doing what makes the most sense
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in the least amount of time.
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When computers face hard problems,
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they deal with them by making them into simpler problems --
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by making use of randomness,
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by removing constraints or by allowing approximations.
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Solving those simpler problems
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can give you insight into the harder problems,
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and sometimes produces pretty good solutions in their own right.
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Knowing all of this has helped me to relax when I have to make decisions.
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You could take the 37 percent rule for finding a home as an example.
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There's no way that you can consider all of the options,
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so you have to take a chance.
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And even if you follow the optimal strategy,
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you're not guaranteed a perfect outcome.
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If you follow the 37 percent rule,
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the probability that you find the very best place is --
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funnily enough ...
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(Laughter)
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37 percent.
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You fail most of the time.
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But that's the best that you can do.
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Ultimately, computer science can help to make us more forgiving
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of our own limitations.
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You can't control outcomes, just processes.
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And as long as you've used the best process,
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you've done the best that you can.
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Sometimes those best processes involve taking a chance --
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not considering all of your options,
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or being willing to settle for a pretty good solution.
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These aren't the concessions that we make when we can't be rational --
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they're what being rational means.
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Thank you.
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(Applause)
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