What did the Stanford prison experiment show?
The Stanford prison study which was conducted by Zimbardo showed that the roles can have a great impact on behavior, thus estimating the power of the situation. It also challenged ethics.
Generally, psychology is shown that we tend to underestimate the power of the situation on behavior and overestimate the personal traits on behavior.
EX: I failed a math test because I had a dance competition. But others assumed that I was bad at math or just plain stupid.
In the prison experiment, young men dressed as wardens and were forced to act as prison wardens or police officers. They made fake arrests (arresting without pressing official charges) of people, brought those people to a cell, and the "police wardens" acted like brutal police officers since they were given the role of police officers. These "police wardens" were innocent until they were given the role as warden or police office thus concluding that roles greatly impacts behavior with the power of the situation.
This challenged ethics as well because these police wardens abused the experimentees by doing inappropriate and unnecessary actions for which these experimentees were not even legally charged.