The Stanford Prison Experiment

In 1971, Philip Zimbardo assigned 24 college students to be either "guards" or "prisoners" in a mock prison in Stanford's basement. Within 36 hours, guards were psychologically torturing prisoners. One prisoner had a breakdown on Day 2. The experiment was supposed to last two weeks; it was terminated after six days. It became the most cited psychology study of the 20th century — and one of the most controversial, with later researchers questioning whether Zimbardo coached the guards' cruelty. Either way, it changed how we think about power forever.