The Great Mental Models (Vol. 2) by Shane Parrish [Summary]

This is a comprehensive summary of the book The Great Mental Models, Volume 2: Physics, Chemistry and Biology by Shane Parrish. Covering the key ideas and proposing practical ways for achieving what’s mentioned in the text. Written by book fanatic and online librarian Ivaylo Durmonski. Supporting Members get full access.

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A noble project aiming to bring more awareness to important thinking concepts. In volume 2 of The Great Mental Models series, Shane Parish is exploring 24 fundamental mental models from physics, chemistry, and biology. Full of stories and great illustrations, this second book will upgrade your mental capacity. You’ll learn how to apply scientific concepts in your normal life. Fill in the gaps in your understanding of the world. And ultimately, make better decisions.

The Core Idea:

Work in accordance with the world, not against it. The mental models presented in this volume will show you how the world works so you can go with the flow of things instead of swimming against the tides of nature’s laws. The physics, chemistry, and biology concepts inside this book explore foundational models that can be applied beyond laboratory tests and scientific papers. The author nicely links science frameworks to social science. You’ll understand both what you need to do in everyday situations and also what you need to avoid doing.


  • In every ecosystem, there are keystone species (or elements in a certain project) that have a disproportionately large effect on its natural environment.
  • To stay alive, we need to continuously adapt to the ever-changing environment.
  • We are energy minimizers – always looking for ways to cut corners and save energy.

6 Key Lessons from The Great Mental Models Vol.2:

Lesson #1: People Interpret the Same Event Differently

We misjudge a situation, not because of the things that are in front of us but because we’re not aware that there are other things, hidden from our sight.

The first concept explored in volume 2 is the theory of relativity.

Shane Parish shares a thought experiment conducted more than 300 years ago – by Galileo Galilei.

What the Italian physicist discovered back then is that when people move at the same speed and in the same direction, they observe the same things. However, they see completely different things when their location, speed, and/or direction are not the same.

The description of the experiment is of a scientist, standing below deck on a ship, who drops a ball from his waist level. The scientist, unable to see the movement of the ship, sees only the vertical movement of the ball. However, since the ship is also moving forward, there is also a horizontal movement that the scientist is unable to capture. Only a person who is not moving, say someone standing on the beach, can see the horizontal movement because his perspective is different.

The concept of relativity helps us understand that different perspectives unlock additional information. If the physical location of two individuals is different, they’ll see different things. And even more interestingly, they will both have correct, but different interpretations of the same event.

Realizing that your perspective may be imperfect a lot of times during the day will make you more empathetic and willing to seek different opinions and points of view. You will stop stubbornly safeguard your opinion and start accepting new viewpoints.

While we all see our own version of events, the goal is to enlarge our perspective to be a closer representation of reality by removing some of the factors that cloud our judgment. One of the best ways to do this is by noticing and observing the details of what is going on around you.” Shane Parrish

Lesson #2: Understand Thermodynamics to Understand How The World Works

The laws of thermodynamics can help us a lot in terms of understanding how the world works on an atomic level.

Once we have the gist – that everything requires energy and nature is in constant pursuit of balance – we can move with more caution. Preserve our energy and also avoid being influenced by external forces that want to impose their views on us.

For starters, it’s useful to consider the four foundational laws of thermodynamics:

  1. Energy is never lost. It can only be transferred from one object, or form, to another. For example, light to heat.
  2. Entropy in the world is always increasing. To create order, we need to exhaust energy.
  3. Entropy in a system approaches zero when the temperature also approaches zero.
  4. The fourth law is called the zeroth law. It was formulated after the above three laws were formed. In short, it states that if two objects exchange no energy, and they are in contact with a third object, there will be no exchange of heat between the three.

Essentially, the laws of thermodynamics are about finding order in the chaotic world.

But the core laws are not the main argument in the book. The metaphorical applications of the laws explained by Shane Parrish are far more interesting for observation and consideration.

For example, regardless of how one thing in nature is far more energy-emitting than another, eventually, the two objects (life forms) will reach a point of mutual existence – equilibrium. Trees, shrubs, animals, parasites all learn to live together in harmony.

Analogically, we can see how different people become the “same” people based on the individuals they regularly see. At some point, if you crowd yourself with the same people without allowing new connections to enter your life, a form of balance will emerge between your views and the views of others – you’ll eventually all think the same way. This means that if we don’t expose ourselves to different concepts and ideas, our mental capacity will always stay the same.

Every new piece of information causes disturbance in your system. At some point, you somehow adopt it. But if you never expose yourself to new behavior traits and new insights, you’ll never grow.

The idea here is that there is value in chaos. If there is only balance, as the author states in the book, “there is no change, no growth, no movement.”

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