Psychology Business Big Ideas

The Great Mental Models: General Thinking Concepts (Summary)

by Shane Parrish and Rhiannon Beaubien

To a man with only a hammer, every problem looks like a nail. A surgeon sees a health problem and wants to cut. A marketer sees the same problem and wants to launch a campaign. An engineer wants to build a better system. Who is right? They all are—and they all are dangerously wrong. Their single tool blinds them to the true shape of the problem. The most effective thinkers don't have one tool; they have a toolbox.

The Map Is Not the Territory

Our understanding of the world is based on simplified models, or 'maps.' These maps are useful, but they are not reality itself. Mistaking the map for the territory—like relying solely on a financial model or a single statistic—can lead to catastrophic errors.

During a training exercise in the Alps, a Hungarian army unit got lost in a blizzard. They were about to give up when a soldier found a map. Using it, they navigated their way out. Only afterward did they realize the map was of the Pyrenees, a completely different mountain range. Their belief in the map, and the action it inspired, was more important than its accuracy, a stark reminder that our models shape our actions, whether they're correct or not.

Reason from First Principles, Not by Analogy

Most people reason by analogy—they do things because that's how they've always been done. First-principles thinking involves breaking a problem down to its most fundamental truths and building a solution from there, free from prior assumptions.

When Elon Musk wanted to build rockets, he was shocked by their multi-million dollar price tag. Instead of accepting the industry price (analogy), he calculated the raw material cost of a rocket (aluminum, titanium, carbon fiber), which was only 2% of the final cost. Realizing this, he decided to build rockets from scratch, which led to the creation of SpaceX and a 10x reduction in the cost of reaching orbit.

Always Ask: 'And Then What?'

First-order thinking looks for the immediate consequence of an action. Second-order thinking, a much rarer skill, asks about the consequences of those consequences. It's about seeing the chain reaction of effects over time to avoid unintended negative outcomes.

To curb the number of venomous snakes in colonial Delhi, the British government offered a cash bounty for every dead cobra. The policy worked at first. But then, enterprising citizens began breeding cobras just to collect the bounty. When the government discovered this and canceled the program, the breeders released their now-worthless snakes, resulting in a cobra population even larger than when they started.

Invert, Always Invert

Often, the best way to solve a problem is to approach it backward. Instead of asking how to achieve a goal (e.g., success), ask what would guarantee the opposite (e.g., failure) and then systematically avoid those things.

To figure out how to be happy, the great stoic philosophers wouldn't make a list of things that bring joy. Instead, they would list all the things that are guaranteed to cause misery—envy, gluttony, dishonesty, fear—and then structure their lives around meticulously avoiding them.

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