在Wikipedia上有很多有用的信息, 摘几段:
Stereotypes focus upon and thereby exaggerate differences between groups. Competition between groups minimizes similarities and magnifies differences. This makes it seem as if groups are very different when in fact they may be more alike than different.
Another theory is that people stereotype because of the need to feel good about
oneself. Stereotypes protect one from anxiety and enhance
self-esteem. By designating one’s own group as the standard or normal group and assigning others to groups considered inferior or abnormal, it provides one with a sense of worth.