We, human beings, are a species that’s not only capable of acting on hidden motives—we’re designed to do it. Our brains are built to act in our self-interest while at the same time trying hard not to appear selfish in front of other people. And in order to throw them off the trail, our brains often keep “us,” our conscious minds, in the dark. The less we know of our own ugly motives, the easier it is to hide them from others. Self-deception is therefore strategic, a ploy our brains use to look good while behaving badly.

So what turns an otherwise rigid, almost robotic dominance hierarchy into something teeming with politics? In a word: coalitions. Allies who wield power together. ... Two-against-one maneuvering is what lends chimpanzee power struggles both their richness and their danger. Coalitions are key. No male can rule by himself, at least not for long.

In light of this, often the best way to get others to believe something is to make it a reality. ... Similarly, often the best way to convince others that we believe something is to actually believe it. ... Faced with the translucency of our own minds, then, self-deception is often the most robust way to mislead others.

Our brains are built to act in our self-interest while at the same time trying hard not to appear selfish in front of other people. And in order to throw them off the trail, our brains often keep “us,” our conscious minds, in the dark. The less we know of our own ugly motives, the easier it is to hide them from others. Self-deception is therefore strategic, a ploy our brains use to look good while behaving badly.

That’s why the best signals—the most honest ones—are expensive. More precisely, they are differentially expensive: costly to produce, but even more costly to fake. ... Sometimes it’s even necessary to do something risky or wasteful in order to prove that you have a desirable trait. This is known as the handicap principle.

The answer is that our thoughts aren’t as private as we imagine. In many ways, conscious thought is a rehearsal of what we’re ready to say to others. As Trivers puts it, “We deceive ourselves the better to deceive others.”

When a group’s fundamental tenets are at stake, those who demonstrate the most steadfast commitment—who continue to chant the loudest or clench their eyes the tightest in the face of conflicting evidence—earn the most trust from their fellow group members. The employee who drinks the company Kool-Aid, however epistemically noxious, will tend to win favor from colleagues, especially in management, and move faster up the chain. In fact, we often measure loyalty in our relationships by the degree to which a belief is irrational or unwarranted by the evidence.