The Lucifer Effect investigates the situational forces that transform good people into perpetrators of evil, challenging a more traditional belief that evil arises from weakness of character or one’s inner nature. Zimbardo argues against this belief by asserting that “situational features” can influence behavior and lead people to commit “ego-alien deeds, as antisocial, as destructive of others” (vii).

The Lucifer Effect advocates adopting a public health model for preventing evil and a reconsideration of legal theory regarding the extent to which situational and systemic factors influence sentencing mitigation. Much of the book is framed negatively and details horrific abuses, but “the deeper message is a positive one” (viii). Zimbardo adopts the same situational perspective to discuss heroism and establishes the same situational dynamics that inflame evil can inspire heroism. 

To fully understand human behavior and prevent undesirable behavior, one must understand the limits of personal power, situational power, and systemic power. Our society currently adopts a medical model approach to curing individual wrongs—treating the perpetrator as if they acted in a vacuum, free of situational and systemic influences. Zimbardo advocates shifting to a public health style approach, treating the problems of undesirable behavior by understanding the situations which cause individual actors to perpetrate offenses and addressing the system in which such offenses are committed.