Humans often engage in irrational behavior. We fight. We start wars. We kill. We are self-destructive. We are petty and vindictive. We "act out" when we don't get our way. We abuse our spouses. We neglect our children. We rationalize, project, and stereotype. We contradict and deceive ourselves in countless ways. We act inconsistently, ignore relevant evidence, jump to conclusions, and say and believe things that don't make good sense. We are our own worst enemy.
The ultimate motivating force behind human irrationality is best understood, we believe, as human egocentrism, the natural human tendency "to view everything within the world in relationship to oneself, to be self-centered" (