People do not decide in isolation. The bandwagon effect is the tendency to adopt beliefs or behaviors because many others have, social proof taken to an extreme. The false consensus effect is a quieter cousin, the overestimation of how much others share one's own views, while its mirror image, the false uniqueness effect, leads people to underestimate how common their good qualities are. Naive cynicism adds a darker twist: people expect more self-interested behavior from others than actually occurs. The third-person effect holds that media and persuasion affect others more than oneself. Each of these can be countered by asking explicitly, surveying, or reasoning from first principles rather than social signal.
Group dynamics introduce systematic distortions of their own. Groupthink, in which members prioritize harmony over critical evaluation, has been implicated in classic failures such as the Bay of Pigs invasion, Vietnam escalation, and the Challenger disaster. Conformity bias was demonstrated in Asch's line experiments, in which roughly 75 percent of subjects conformed to an obviously wrong group answer at least once. Obedience to authority, famously documented in Milgram's shock experiments, where about 65 percent of subjects administered the maximum apparent shock under instruction, shows how readily personal values yield to perceived authority. Authority bias more generally causes over-weighting of input from authority figures regardless of its relevance, and is countered by separating identity from argument quality.
Diffusion of responsibility underlies the bystander effect: the presence of others dilutes individual responsibility, reducing the likelihood that any one person will help in an emergency. The Kitty Genovese case prompted this research, though later scholarship noted that the original details were partly mythologized. Assigning explicit responsibility is the standard remedy. Reciprocity bias and the foot-in-the-door and door-in-the-face techniques show how compliance escalates through small commitments, unsolicited gifts, and contrasting requests, with the Ben Franklin effect noting that someone who has done you a favor is more likely to do another than someone you have favored.