In social psychology, pluralistic ignorance is a situation in which a majority of group members privately reject a norm, but go along with it because they assume, incorrectly, that most others accept it. This is also described as “no one believes, but everyone thinks that everyone believes”. Pluralistic ignorance is a bias about a social group, held by the members of that social group.
Pluralistic ignorance may help to explain the bystander effect. If no-one acts, onlookers may believe others consider taking action to be improper, and may therefore themselves refrain from acting.