What is the groupthink bias?

In a cohesive group, the desire for harmony and consensus overrides realistic appraisal, so people suppress doubts and dissent to avoid rocking the boat.

The mechanism is social pressure plus comfort: disagreeing risks conflict and exclusion, agreeing feels safe and affirming, so members self-censor, assume silence means consent, and converge on a decision no individual would defend alone. Critical thinking is traded for group cohesion.

Example: In a meeting where everyone seems on board, the one person who senses a flaw stays quiet — assuming "if it were really a problem, surely someone smarter would have said so." Several people may be thinking exactly that, and a bad plan sails through unchallenged.

Tip: Assigning a formal "devil's advocate," or having people write opinions down before discussion, breaks the silence-equals-agreement spiral.