Give people roles, and they will quickly start playing them. Everybody plays a role in our world, and most of the people are totally caught in that role, forgetting that they are humans above all. Their "masks" take over them
Stanford experiment :
http://en.wikipedia.org/wiki/Stanford_prison_experiment
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')The experiment was conducted in 1971 by a team of researchers led by psychologist Philip Zimbardo at Stanford University. Undergraduate volunteers played the roles of both guards and prisoners living in a mock prison in the basement of the Stanford psychology building.
The experiment quickly grew out of hand. Prisoners suffered — and accepted — sadistic and humiliating treatment from the guards. The high level of stress progressively led them from rebellion to inhibition. By experiment's end, many showed severe emotional disturbances.
After a relatively uneventful first day, a riot broke out on the second day. The guards volunteered to work extra hours and worked together to break the prisoner revolt, attacking the prisoners with fire extinguishers without supervision from the research staff.
Prisoner counts, initially devised for the prisoners to learn their identity numbers, degenerated to hour-long ordeals where guards tormented the prisoners and imposed physical punishments, including long bouts of forced exercise. The prison became dirty and inhospitable; bathroom rights became privileges, which could be, and frequently were, denied. Some prisoners were forced to clean toilets with bare hands. Mattresses were removed from the "bad" cell block and the prisoners forced to sleep naked on the concrete floor. Moreover, prisoners endured forced nudity and even sexual humiliation.
Zimbardo cited his own absorption in the experiment he guided, and in which he actively participated as Prison Superintendent. On the fourth day, he and the guards reacted to an escape rumor by attempting to move the entire experiment to a real, unused cell block at the local police station, because it was more secure. The police department refused, citing insurance liability concerns; Zimbardo recalls his anger and disgust with the lack of co-operation, between his and the police's jails.
As the experiment proceeded, several guards became progressively sadistic. Experimenters said that approximately one-third of the guards exhibited genuine sadistic tendencies. Interestingly, most of the guards were upset when the experiment concluded early.