Philip Zimbardo's most famous study, The Stanford Prison Experiment, almost went horribly wrong.
The experiment had to be called off within a week because the conditions had proved to be too dangerous for participants to continue.
Psychologists have a duty to protect their participants from mental and physical harm and, as you will see, Zimbardo's study put both of these at risk.
A plaque is still mounted on the wall at Stanford University where the study took place.
If the study goes to show us anything, it is that we should always be aware of social and situational influences which may pressure us to behave in ways we might otherwise not.