Here’s the most important thing I ever learned about the way we see the world and process information…. The brain is in charge of two very different goals:

1. Successfully move our bodies around through space and time (accomplish tasks needed for survival)

2. Use as little energy as possible. Even though it accounts for 2% of our weight, the brain uses about 20% of our body’s energy. Unless we’re really motivated—given extra rewards, or come across a mistake we can’t avoid—we conserve energy.

Ergo, the Law of Least Effort

In Thinking, Fast and Slow by Nobel Prize-winning researcher Daniel Kahneman, here’s a primer: we do the “thinking fast” bit unless we really, really have to.

Thinking Fast = System 1, our automatic, intuitive mind that usually lets us navigate the world easily and successfully; habitual, model-free thinking (actions → outcome, regardless of where we are).
Thinking Slow = System 2, our controlled, deliberative, analytical mind; model-based and goal-directed (takes other things into account)

So, to repeat: our brain appears to view controlling itself—or thinking—as a cost: it will only use System 2 to think deeply, learn something new, and update itself when it has to, when there’s real value.

Another function of System 2 (slow) is to monitor System 1 (fast): we’ll learn when we have no choice but to confront a mistake, which means that it does a miraculous job of avoiding situations when it could be at fault. Why? From our brain’s perspective, finding out that we’ve made a mistake is tiring, because it means that we have to adjust the controls, and reconfigure how we make sense of the world.

The idea that thinking itself is a cost leads to the most common cognitive error, the focusing illusion, commonly referred to as WYSIATI: What You See Is All There Is.

We all view the world like a fisheye lens.

This makes sense from a survival standpoint: we have to focus on what’s right around us. From our perspective, we are always at the center of the world. Everything is right in front of us; thinking of anything else takes work.