What is groupthink and how can it be prevented?

Groupthink, identified by Irving Janis, is a phenomenon where the desire for harmony and conformity in a group leads to irrational or dysfunctional decision-making. Group members suppress dissent, ignore alternatives, and develop an illusion of invulnerability and moral superiority. Historical examples include the Bay of Pigs invasion and the Challenger disaster. Prevention includes assigning a devil's advocate, encouraging all members to voice concerns, inviting outside experts, and having the leader withhold their opinion initially to avoid anchoring the discussion.