In 1970 Phillip Zimbardo, Ph.D. Psy., conducted an experiment. Setting up a prison atmosphere, he asked for student volunteers to assume roles as guards or prisoners and he assumed the role of warden. In one day he discovered that the guards became aggressive and cruel, and the prisoners intimidated and submissive. Moreover, he discovered he had lost his perspective during the onset of the experiment and found himself invaginated in his role as warden. Instead of two weeks, the experiment was reduced to one day.

MORE INFO:

http://www.stanford.edu/dept/news/relaged/970108prisonexp.html

http://www.geocities.com/BourbonStreet/Delta/8818/milgram.htm