The Great Mental Models Volume 3 summary

Say you’re walking down the street when you bump into a friend. What do you do? You probably won’t just ignore him and walk on. You’d be fully within your rights to do so, but then your friend would be upset. So, to avoid negative reactions, you’re more likely to stick to social norms like saying hello. 

Feedback loops – including things like social disapproval – are a common component of many systems in daily life. In fact, feedback loops serve as the basis for all civilization. Once you start looking for them, they’ll appear everywhere. Tuning into how they work as a mental model can help you tweak your behavior to be more successful.

Maybe you’ve heard of the Trans-Siberian Railway – also known as the longest railway in the world. At 9,500 kilometers, it spans all of Russia, from St. Petersburg to just east of North Korea. So, as you can imagine, when the Russian state began building it in the late nineteenth century, the scope of the project was so great that delays were inevitable. 

There was a continual shortage of construction supplies. As soon as that was fixed, weather-affected delays took hold. Once the weather improved, a physical barrier came up: there was a massive lake in the middle of the planned railway that would call for a total redesign of the route. In fact, the first Trans-Siberian track was rendered almost unusable, and Russia had to rebuild the railway multiple times. 

Imagine you’ve just gotten a drug prescription from your doctor. It has two main components: the medicine you’re supposed to take, and how much of it you need to treat your ailment.

To determine the right dosage for your treatment, pharmacologists have to make two calculations. First, they calculate the lowest possible amount of a medication that can achieve a meaningful benefit. Next, they calculate the largest amount the average patient could take without suffering harm. 

Let’s say someone asks you to press “enter” on your keyboard every minute, for eight hours a day. Doesn’t sound like a terribly exciting way to spend your time, does it? For most people, engaging in repetitive actions over and over again gets boring very quickly. 

That’s why we codify machines to do tasks for us. To tell those machines what to do, like press a button every minute, we use one of the most important models in human civilization: the algorithm. 

Have you ever had one of those days where everything seems to go wrong? In the span of a few hours, you lose your phone, stub your toe, get a parking ticket, and drop your groceries in a puddle. It would be easy to think the world is out to get you. 

But this is just an illusion. 

Maybe you have a savings account. You know that the longer you leave that money untouched, the more savings you’ll have. This is thanks to the concept of compound interest. 

Compounding is a core mental model of financial systems. It indicates that the longer you let your gains compound, the more dramatically they will increase. 

Imagine you want to investigate the color of swan populations. If you go out to your neighborhood ponds to collect data, you might conclude that all swan populations are white. But if you were to expand your research sample and study a larger number of swans from across the country, you would discover that some are actually black. 

When you want to get representative information about a population, you usually need to look at a sample – meaning a part of that population. But if that sample is not truly representative, you risk being misled.