Even if we take Nietzsche figuratively (which he would have much preferred anyway), fifty years of research on stress shows that stressors are generally bad for people,3 contributing to depression, anxiety disorders, and heart disease.

It is easy to see the faults of others, but difficult to see one’s own faults. One shows the faults of others like chaff winnowed in the wind, but one conceals one’s own faults as a cunning gambler conceals his dice.5

People who are told that they have performed poorly on a test of social intelligence think extra hard to find reasons to discount the test; people who are asked to read a study showing that one of their habits — such as drinking coffee — is unhealthy think extra hard to find flaws in the study, flaws that people who don’t drink coffee don’t notice. Over and over again, studies show that people set out on a cognitive mission to bring back reasons to support their preferred belief or action. And because we are usually successful in this mission, we end up with the illusion of objectivity. We really believe that our position is rationally and objectively justified.

If people are like plants, what are the conditions we need to flourish? In the happiness formula from chapter 5, H(appiness) = S(etpoint) + C(onditions) + V(oluntary activities), what exactly is C? The biggest part of C, as I said in chapter 6, is love. No man, woman, or child is an island. We are ultrasocial creatures, and we can’t be happy without having friends and secure attachments to other people. The second most important part of C is having and pursuing the right goals, in order to create states of flow and engagement. In the modern world, people can find goals and flow in many settings, but most people find most of their flow at work.

With such a vast and wonderful library spread out before us, we often skim books or read just the reviews. We might already have encountered the Greatest Idea, the insight that would have transformed us had we savored it, taken it to heart, and worked it into our lives.

Increase similarity, not diversity. To make a human hive, you want to make everyone feel like a family. So don’t call attention to racial and ethnic differences; make them less relevant by ramping up similarity and celebrating the group’s shared values and common identity.49 A great deal of research in social psychology shows that people are warmer and more trusting toward people who look like them, dress like them, talk like them, or even just share their first name or birthday.50 There’s nothing special about race. You can make people care less about race by drowning race differences in a sea of similarities, shared goals, and mutual interdependencies.51

We should not expect individuals to produce good, open-minded, truth-seeking reasoning, particularly when self-interest or reputational concerns are in play. But if you put individuals together in the right way, such that some individuals can use their reasoning powers to disconfirm the claims of others, and all individuals feel some common bond or shared fate that allows them to interact civilly, you can create a group that ends up producing good reasoning as an emergent property of the social system. This is why it’s so important to have intellectual and ideological diversity within any group or institution whose goal is to find truth (such as an intelligence agency or a community of scientists) or to produce good public policy (such as a legislature or advisory board).

Keep your eye on the intuitions, and don’t take people’s moral arguments at face value. They’re mostly post hoc constructions made up on the fly, crafted to advance one or more strategic objectives.

So the next time a salesman gives you a free gift or consultation, or makes a concession of any sort, duck. Don’t let him press your reciprocity button. The best way out, Cialdini advises, is to fight reciprocity with reciprocity. If you can reappraise the salesman’s move for what it is — an effort to exploit you — you’ll feel entitled to exploit him right back. Accept the gift or concession with a feeling of victory — you are exploiting an exploiter — not mindless obligation.

If people can’t satisfy their need for deep connection in other ways, they’ll be more receptive to a smooth-talking leader who urges them to renounce their lives of “selfish momentary pleasure” and follow him onward to “that purely spiritual existence” in which their value as human beings consists.

The authors pointed out that nearly all research in psychology is conducted on a very small subset of the human population: people from cultures that are Western, educated, industrialized, rich, and democratic (forming the acronym WEIRD). They then reviewed dozens of studies showing that WEIRD people are statistical outliers; they are the least typical, least representative people you could study if you want to make generalizations about human nature. Even within the West, Americans are more extreme outliers than Europeans, and within the United States, the educated upper middle class (like my Penn sample) is the most unusual of all.

If you ask people to sing a song together, or to march in step, or just to tap out some beats together on a table, it makes them trust each other more and be more willing to help each other out, in part because it makes people feel more similar to each other.