Forty years ago researchers at Stanford University conducted a controversial experiment, creating a fake jail, using volunteers to act as prisoners and guards: The Stanford Prison Experiment. Less than halfway through, the situation got out of hand, as the jailed volunteers, reacting to abuse from the volunteer guards, began to revolt and crack. The researchers let the situation deteriorate for six days until one finally spoke out. For the anniversary of the experiment, Romesh Ratnesar interviewed some of the participants for Stanford Magazine, giving us insight into what kept things running, even as things completely devolved.

Phil Zimbardo Superintendent: In Denial A professor in Stanford’s psychology department, Zimbardo acted the part of superintendent, overseeing the prison's authority. At the beginning of the experiment, the participants didn't take to their parts, "After the end of the first day, I said, 'There's nothing here. Nothing's happening.' The guards had this anti-authority mentality. They felt awkward in their uniforms. They didn't get into the guard mentality until the prisoners started to revolt," explains Zimbardo. While the guards transformed into brutal figures and the prisoners into victims, this mentality didn't change for Zimbardo, "Throughout the experiment, there was this conspiracy of denial—everyone involved was in effect denying that this was an experiment and agreeing that this is a prison run by psychologists."

Even his girlfriend at the time, fellow Stanford graduate student Christina Maslach, tried to get him to snap out of it. Zimbardo recalls an argument the two had, where she points out the injustices, "It's terrible what you're doing to these boys. How can you see what I saw and not care about the suffering?" But, even then, both his denial and the experiment continued, "But I didn't see what she saw." Influenced by Maslach, eventually Zimbardo ended the study. In love with each other, Maslach kept pushing Zimbardo to reconsider, "because this was someone I was growing to like a lot, I thought that I had to figure this out.It's an interesting question: Suppose he kept going, what would I have done? I honestly don't know."

Dave Eshelman, Guard: Just Playing the Part He answered the ad hoping to find interesting summer work but felt it was important to take his role seriously. He very much planned his unsavory demeanor,

What came over me was not an accident. It was planned. I set out with a definite plan in mind, to try to force the action, force something to happen, so that the researchers would have something to work with. After all, what could they possibly learn from guys sitting around like it was a country club? So I consciously created this persona.

Here we see how seriously the guards took their roles:

Richard Yacco, Prisoner: I Did It For Science's Sake Yacco helped instigate the revolt below and researchers later released him early after he exhibited signs of depression. Yacco explains his participation  When I asked [Zimbardo's team] what I could do if I wanted to quit, I was told, "You can't quit--you agreed to be here for the full experiment."

Ratnesar, whose day job is the deputy editor of Bloomberg Business Week, has much more from the participants and his full story is well worth the read.