In the summer of 1971, Philip Zimbardo, Craig Haney, and Curtis Banks carried out a psychological experiment to test a simple question: What happens when you put ordinary people in positions of power, enabling abuse? Does humanity win over evil, or does evil triumph? To explore this, student volunteers were selected and randomly assigned to play the role of prisoner or guard in a simulated prison at Stanford University. Although the students were mentally healthy and knew they were taking part in an experiment, some guards quickly became sadistic, while prisoners showed signs of acute stress, depression and trauma. After only six days, the planned two-week study was a disaster...