Pluralistic ignorance occurs when individuals in a group mistakenly believe that their private thoughts, feelings, or behaviors are different from those of the group, often leading to a reinforcement of a norm that no one actually supports. This phenomenon can perpetuate social norms or behaviors because everyone assumes others agree with them, even when they privately disagree.
Diffusion of responsibility is a social psychology phenomenon where individuals are less likely to take action or feel accountable when others are present, often leading to inaction in emergency situations. This effect is amplified in larger groups, as people assume someone else will intervene or is better suited to respond.