GroupThink

Type I: Overestimations of the group—its power and morality

1. Illusions of invulnerability creating excessive optimism and encouraging risk taking.
2. Unquestioned belief in the morality of the group, causing members to ignore the consequences of their actions.

Type II: Closed-mindedness

1. Rationalizing warnings that might challenge the group's assumptions.
2. Stereotyping those who are opposed to the group as weak, evil, biased, spiteful, impotent, or stupid.

Type III: Pressures toward uniformity

1. Self-censorship of ideas that deviate from the apparent group consensus.
2. Illusions of unanimity among group members, silence is viewed as agreement.
3. Direct pressure to conform placed on any member who questions the group, couched in terms of "disloyalty"
4. Mind guards — self-appointed members who shield the group from dissenting information.

ways to avoid GroupThink:

1. Leaders should assign each member the role of “critical evaluator”. This allows each member to freely air objections and doubts.
2. Higher-ups should not express an opinion when assigning a task to a group.
3. The organization should set up several independent groups, working on the same problem.
4. All effective alternatives should be examined.
5. Each member should discuss the group's ideas with trusted people outside of the group.
6. The group should invite outside experts into meetings. Group members should be allowed to discuss with and question the outside experts.
7. At least one group member should be assigned the role of Devil's advocate. This should be a different person for each meeting.

The main principle of groupthink, which I offer in the spirit of Parkinson's Law, is this: The more amiability and esprit de corps there is among the members of a policy-making ingroup, the greater the danger that independent critical thinking will be replaced by groupthink, which is likely to result in irrational and dehumanizing actions directed against outgroups.

Bay of Pigs invasion
The United States Bay of Pigs Invasion was one of the primary political case studies that Janis used in explaining the theory of groupthink. The invasion plan was initiated by the Eisenhower administration, but when the Kennedy White House took over, it "uncritically accepted" the CIA's plan.When some people, such as Arthur M. Schlesinger, Jr. and Senator J. William Fulbright, attempted to present their objections to the plan, the Kennedy team as a whole ignored these objections and kept believing in the morality of their plan. Eventually Schlesinger minimized his own doubts, that is, he performed self-censorship.The Kennedy team stereotyped Castro and the Cubans by failing to question the CIA about its many assumptions, including the ineffectiveness of Castro's air force, the weakness of Castro's army, and the inability of Castro to quell internal uprisings. Janis claimed the fiasco that ensued could have been prevented if the Kennedy administration had followed the methods to preventing groupthink that it followed later during the Cuban Missile Crisis.

 Pearl Harbor

The attack on Pearl Harbor on December 7, 1941 was a prime example of groupthink. A number of factors such as shared illusions and rationalizations contributed to the lack of precaution taken by Naval officers based in Hawaii. The United States had intercepted Japanese messages and they discovered that Japan was arming itself for an offensive attack. Washington took action by warning officers stationed at Pearl Harbor, but their warning was not taken seriously. They assumed that Japan was taking measures in the event that their embassies and consulates in enemy territories were usurped.
The Navy and Army in Pearl Harbor also shared rationalizations about why an attack was unlikely. Some of them included:

• "The Japanese would never dare attempt a full-scale surprise assault against Hawaii because they would realize that it would precipitate an all-out war, which the United States would surely win."
• "The Pacific Fleet concentrated at Pearl Harbor was a major deterrent against air or naval attack."
• "Even if the Japanese were foolhardy to send their carriers to attack us [the United States], we could certainly detect and destroy them in plenty of time."
• "No warships anchored in the shallow water of Pearl Harbor could ever be sunk by torpedo bombs launched from enemy aircraft."

thanks to Irving Janis and Wikipedia