The Great Mental Models Book Summary - The Great Mental Models Book explained in key points

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The Great Mental Models summary

Name: The Great Mental Models
Rating: 4.5 (349 reviews)
Author: Shane Parrish and Rhiannon Beaubien

Shane Parrish and Rhiannon Beaubien

General Thinking Concepts

4.5 (349 ratings)

26 mins

Table of Contents

The Great Mental Models
summarized in 9 key ideas

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Key idea 1 of 9

What’s in it for me? Upgrade your mental toolkit and make better decisions.

In most areas of life, you need the right tools to get the job done. Want to fix a clogged toilet? Get a plunger. Want to write a novel? Grab a pen. The more complicated the job, the more tools you’ll tend to need. Just look at all the gear inside the workshop of a car mechanic.

The same is true of decision-making – only here, the tools you need are mental devices. To make good decisions in life, you need to think through your options carefully. Certain ideas, techniques and knowledge can help you out with this. How? By enabling you to create a better working model of reality in your mind. We can therefore call them mental models.

The better your models, the better your chances of success. And the more varied your models, the more prepared you’ll be to handle the many challenges life throws your way. Ideally, you’d have a whole toolbox full of mental models – and that’s exactly what you’re about to receive: not just one, not just two, but nine of the most useful mental models for making better decisions!

In these blinks, you’ll learn about

a zany thought experiment that helped Einstein understand gravity;
the dark secrets of a 1920s propaganda pioneer; and
the difference between Occam’s razor and Hanlon’s razor.

A map is a simplified representation of a complicated reality.

Mental models are tools that help us navigate reality. The most obvious example is a map. As familiar as it might seem, this classic navigational aid illustrates some of the basic features, benefits, and limits of mental models in general. So it’s a good place to start.

The purpose of a map is to represent the world in a way that’s useful to us. To accomplish this purpose, a map needs to focus on certain aspects of reality while ignoring everything else. For instance, if you’re trying to navigate the London Underground, all you need is a map that shows the overall layout of the subway’s rails and stations – the information that will help you get to your destination. A simple array of lines and circles will do the trick.

The key message here is: A map is a simplified representation of a complicated reality.

Of course, the resulting map – that network of lines and circles – leaves out a lot of details. But that’s unavoidable. To see why, imagine trying to create a map that shows every little detail of the London Underground, right down to the nuts and bolts of the railroad tracks. Such a map would be completely impractical – way too big to fit inside your pocket, and way too complicated to help you get from point A to point B!

So we don’t want a map to include every aspect of the reality it represents. But we also don’t want to forget that it leaves out a lot of details. Sure, many of them are irrelevant to us, like the nuts and bolts of the railroad tracks. But some of them are important to keep in mind. If you’ve ever been so busy looking down at your smartphone map that you walked straight into a lamppost, then you know this firsthand. Or if your GPS device has ever led you to a road that’s closed, then you know the importance of having a map that’s fully up-to-date.

These lessons apply not just to literal maps, but to more metaphorical maps as well. Financial statements, policy papers, parenting manuals, even news articles – they all offer map-like simplifications of reality. A company’s financial statement, for instance, condenses thousands of transactions into a single, easily digestible document.

These simplifications are meant to guide us through the complicated world around us. But if we forget about what they’re leaving out of the picture, and if we fail to update them as the world changes, they can also lead us astray and get us into trouble.

Recognize the limits of your circle of competence.

Imagine all of our practical human knowledge as forming a vast and varied landscape, encompassing everything from knowing how to cook to knowing how to invest in the stock market to knowing how to climb Mount Everest. To navigate most of this terrain, you'll need a map – whether it takes the form of a cookbook, an investment manual, or a mountaineering guide.

Other places, though, will be so familiar to you that a map becomes unnecessary. These places are the skills you’ve mastered through years of study, practice, and hard work – and they all fall within your circle of competence.

Solve problems creatively by reasoning from first principles.

When you focus on your circle of competence, you’re playing to your strengths. But there’s more to success than mere competency. You also need creativity. It might sound like a cliché, but it’s true: you have to think outside the box. Otherwise, you’ll end up doing the same old thing that everyone else is doing. But how do you break away from the pack?

The trick lies in digging deep. For any subject or body of knowledge, if you drill down deep enough, you’ll eventually find what you’re looking for.

Develop your creative problem-solving skills even further by practicing inversion.

Imagine you’re an advertising executive working for the American Tobacco Company in the 1920s. The company has noticed that most smokers are men, and you’ve been tasked with the following objective: sell more Lucky Strike cigarettes to women. Putting aside any moral scruples, how would you achieve this goal?

That was the question once faced by Edward Bernays – the Austrian-American pioneer of the fields of public relations and propaganda. He answered it by implementing the next mental model we’re going to look at. It’s a nifty little trick called inversion, which involves taking the normal approach to problem-solving and turning it upside down.

Use thought experiments to test out your ideas and clarify your thinking.

Now that you’ve learned first-principle reasoning and the technique of inversion, there’s no limit to how many creative ideas you can come up with. Hopefully they’ll be more like growing artificial meat than getting people to smoke! But before you try them out in the real world, you’ll probably want to simulate them in your imagination first.

The key message here is: Use thought experiments to test out your ideas and clarify your thinking.

Engage in second-order thinking to scrutinize your decisions and bolster your arguments.

Imagine you’ve just won the lottery! What’s the first thing you’d do? Let’s say you buy a bigger house. Great – but now you have to consider how this decision will change your life. For example, you might have to spend more time cleaning. Either that, or have to hire a cleaner.

Either way, you’ve now gone from thinking about the consequences of something, as you do when conducting a thought experiment, to thinking about the consequences of the consequences. This is called second-order thinking.

Use probabilistic thinking to weigh your decisions more precisely.

Second-order consequences can often come as an unpleasant surprise. But that doesn’t mean you should get too carried away guarding against them. With any given action, you can imagine all sorts of horrible things happening. If you fixate on them, though, you may become paralyzed with indecision, or overreact by drawing extreme conclusions.

Call it the slippery slope effect. One moment, you’re thinking about all the potential negative consequences of drinking alcohol, such as alcoholism. Next thing you know, you’re advocating for prohibition! That would be an overreaction. Sure, drinking alcohol can lead to alcoholism, but it doesn’t always. To temper our fears and assess the potential consequences of an action rationally, we need to think about their probabilities.

According to Occam’s razor, the simplest of two or more equally compelling explanations is the most likely to be true.

Imagine you wake up one morning feeling sick. Naturally, you go online and look up your symptoms – which, you discover, could either be caused by the flu or by Ebola. Which explanation should you believe? The answer is important. It’s the difference between going back to bed or going into quarantine.

In a situation like this, you’re no longer just weighing an individual piece of evidence, as you do with probabilistic thinking. Now you need to decide between two overall explanations for the evidence you have at hand.

According to Hanlon’s razor, the simplest and most likely explanation for misbehavior is stupidity, rather than malice.

From deadly illnesses to mere tardiness, Occam’s razor provides a great way to decide between competing explanations of things. But the vagaries of human behavior are varied, and sometimes we’ll need another type of blade. This brings us to our final mental model: Hanlon’s razor.

You can think of Hanlon’s razor as a close cousin to Occam’s razor. Like its more famous relative, Hanlon’s razor starts by reminding us that the simpler explanation – all other things being equal – tends to be the safest bet. But then it adds a special twist.

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What is The Great Mental Models about?

The Great Mental Models (2019) provides a crash course on how to upgrade your thinking and decision making. Drawing from a wide variety of disciplines, it will equip you with nine of the most essential tools for understanding and navigating the complicated world around you.

Who should read The Great Mental Models?

Decision makers
Analysts
Anyone who wants to give their thinking an edge

About the Author

Shane Parrish is a former cybersecurity expert who worked for the Communications Security Establishment (CSE) – an agency of Canada’s Department of National Defence. He is host of The Knowledge Project podcast and the founder of Farnam Street – an online learning community and blog. Rhiannon Beaubien is also a former member of the CSE and writes for Farnam Street’s blog.

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