In the 1970s, psychologist Philip Zimbardo recruited a group of young men to pose as guards and prisoners. The guards received no formal training – just instructions to guard the prisoners. Although The Stanford Prison Experiment was meant to take place over the course of two weeks, it was cut short.
Why did it get shut down? Allegedly, the guards took the role so seriously that they began to act cruelly toward the prisoners. Zimbardo asked the guards not to resort to physical violence, but they did. By the sixth day of the experiment, the prisoners had threatened to overthrow the guards. One prisoner stopped eating. Another had a breakdown. Yet, it took six days to call the whole experiment off.