Meet "network man." He has basic desires of his own, but has many arbitrary preferences, such as in music or clothes, that have been influenced by the people he knows. Network man's likes and dislikes, in turn, affect the behavior of his friends, and their friends, and their friends.
People have profound influences on each other's behavior within three degrees of separation, the authors find. That means that your friends, your friends' friends, and your friends' friends' friends may all affect your eating habits, voting preferences, happiness, and more. At the fourth degree, however, the influence substantially weakens.