Think of the last time you experienced an emotion. Love, hate, fear, anger, embarrassment; it doesn't matter which. Where were you and what were you doing? What was it that excited, pleased, or upset you? Chances are there was at least one other person around (even if only in your otherwise private thoughts), and that something that they did or didn't do (or something that was done or not done to them) was part of what made you emotional. Now think about what happened next. Perhaps someone else reacted to your emotion, tried to calm you down, or responded with antagonism. Later still, maybe you discussed your feelings with someone close to you. Maybe, in some ways, the experience affected other people almost as much as it affected you.
What is it about people's behavior that causes emotional effects? Why should some things they do matter to us whereas others do not? How do we tell what is emotionally important? This book proposes that one answer is that we make reference to others' reactions to whatever is happening, especially when we share relationships or affiliations with those others. We know we should care about something at an emotional level if people close to us also seem to care. Further, to the extent that we are members of a common society, we have also learned to perceive, interpret, and act toward things in broadly similar ways, to recognize their conventional significance, and this too partly determines their emotional power. Those raised in different cultural contexts might not always share our emotional perspective on events.