This document discusses four social phenomena related to behaviors in groups: groupthink, group polarization, social facilitation, and social loafing. Groupthink occurs when the desire for group harmony results in irrational decision making. It can be prevented by encouraging alternative perspectives, critical evaluation of ideas, and outside feedback. Group polarization means groups make more extreme decisions than individuals, becoming riskier if initially risky and more cautious if initially cautious. It can be prevented by allowing minority views, limiting concern for feelings, assembling diverse groups, and ensuring interaction among members.