Situationism is a psychological theory that places emphasis on external and situational factors in personality and behavior. Rather than focusing on the importance of innate traits on influencing personality situationists believe that the current and immediate situation is the most influential. Because behaviors change in different scenarios situationism focuses on how the situational and environmental factors influence behavior.
Studies like the Stanford Prison Experiment (where normal people who were randomly chosen as a prison “guard” started to exhibit aggressive and punitive behaviors towards the participants randomly assigned to be “prisoners”) are often cited as supporting evidence that situational factors are the most influential determining qualities for personality.