Groupthink is most likely in groups that are cohesive, insulated and led by someone who states a preference early. Why would cohesion - usually a strength - become a liability for decision quality?

A. Because cohesion raises the cost of dissent.

Cohesion does not remove disagreement; it raises the price of expressing it, and the doubter risks their standing. The damage compounds because the group reads the silence as consensus, pluralistic ignorance from the bystander lesson, applied to a boardroom. Every remedy works by lowering the cost of dissent, and Janis derived them from one administration with and without the safeguards.