Can you give us some context please? Zimbardo usually refers to the Stanford Prison Experiment, a psychology study carried out by professor Philip Zimbardo in the 1970s. In it, a group of students were split into prisoners and guards, and encouraged to play those roles. The guards displayed highly authoritarian and even sadistic behaviours, going beyond those encouraged by the experimenters. The analogies to the Holocaust should be clear. There are, however, some major criticisms levelled at the study, mostly centering around selection bias and the experimental format. Zimbardo was not a neutral observer, as he acted as 'prison supervisor', and hence may have skewed the results. In addition, the advert for the experiment may have encouraged already authoritarian students to apply for it, rather than being representative.