There are a few psychological studies that have such an impact as to reach the public as well as an academic sphere. Milgram's famous obedience studies are just such cases.
Stanley Milgram was interested in understanding what drove ordinary men and women to commit heinous acts during the Second World War. One hypothesis was that obedience to authority and deference could overwrite a social conscience.
The experiment is described in the video at the end of this introduction.
Previous work by Adorno strove to explain horrors such as those in war by looking at authoritarian personality types, though this trait was explained via psychodynamic theories.
What made Milgram's studies so revolutionary was the divergence from common wisdom that they showed. Almost nobody asked in a poll held before the studies guessed the outcome of the experiments. Most people suggested that the shocks would not reach higher levels. What Milgram's experiments showed was that given the appropriate circumstances people could go against their natural inclinations and inflict what they think are extremely painful (even life-threatening) shocks.
Despite the criticisms leveled against the methodology, Milgram performed briefings and follow-ups were with the participants which was not at all commonplace in the 60s. Even so, experiments like those of Milgram's could not be done today, though for replication researchers have found many ingenious ways of mimicking the studies.
For a brief look check out this Youtube video describing in brief Milgram's fascinating experiments:
https://www.youtube.com/watch?v=FEaKl5_Nn3w