Why Do People form Groups,and why do they feel so strongly about them? Consider the celebrations that follow a sports team's winning a national championship.Fans have staked their own self-image on the performance of someone else.The winner,s supporters are elated, and sales of team-related shirts,jackets, and hats declaring support for the team skyrocket.Fans of the losing team feel dejected, even embarrassed. Our tendency to take personal pride or offense for the accomplishments of a group is the territory of social identity theory.