Groupthink — option 2. The phrase “the norm for consensus overrides the realistic appraisal of alternative courses of action” is the standard definition.

The concept. Irving Janis coined the term after studying foreign-policy fiascos — Pearl Harbor, the Bay of Pigs, the escalation in Vietnam. In a cohesive group under pressure, the wish to preserve agreement becomes stronger than the wish to reach the right answer, so doubts are suppressed and alternatives are never seriously examined.

Groupshift, the sharpest distractor. A different phenomenon — group discussion exaggerates the members’ initial leaning, so the group decision is more extreme than the average individual position. It is usually a shift toward greater risk, and is also called group polarisation. Groupthink is about suppressed disagreement; groupshift is about amplified inclination.

The other two are remedies, not diseases. Brainstorming generates ideas with criticism deliberately withheld; the nominal group technique has members write independently and rank in silence before discussing, so no one can dominate. The Delphi technique goes further, keeping experts anonymous and physically apart.

How groupthink is prevented in practice: keep the leader’s own view out of the discussion until others have spoken, appoint a devil’s advocate, use dialectical inquiry with two rival plans, invite outside experts, split into independent sub-groups, and hold a “second-chance” meeting before committing. Each measure reintroduces the disagreement that cohesion suppressed.

Hence, the answer is Groupthink.