Groupthink, a concept introduced by Irving Janis, in his 1972 book “Victims of Groupthink" is a mode of thinking that most people in a cohesive group demonstrate, where the concern for unanimity overrides the motivation to make a realistic application of alternative courses of action.
Groupthink ranks amongst the major flaws of group decision making as it leads to group pressure, which causes deterioration of mental efficiency, reality testing, and moral judgment, and leads to group members developing illusions of invincibility, rationalizing warnings and negative feedback, putting pressure or ostracizing dissenters, and practicing “self-censorship" when their ideas deviate from that of the group.
Individuals in groups tend to conform to the seemingly dominant view in the group and rarely take the courage to dissent. One or two vocal and persuasive members or the selected group leader can very easily dominate the group and drown out the voice of other members, and that of experts. This stifles the consideration of alternative course of actions, the very purpose for which group decision-making takes place.
Groupthink is the result of the subconscious longing for social affinity and aversion or avoidance of social challenges.