Janis Originally Defined Groupthink as "a Mode of Thinking That People Engage in When They Are Deeply Involved in a Cohesive In-Group,

Janis originally defined groupthink as "a mode of thinking that people engage in when they are deeply involved in a cohesive in-group, when the members' strivings for unanimity override their motivation to realistically appraise alternative courses of action." According to his definition, groupthink occurs only when cohesiveness is high. It requires that members share a strong "we-feeling" of solidarity and desire to maintain relationships within the group at all costs. When colleagues operate in a groupthink mode, they automatically apply the "preserve group harmony" test to every decision they face."

Janis consistently held that the "superglue" of solidarity that bonds people together often causes their mental process to get stuck. Janis was convinced that the concurrence-seeking tendency of close-knit groups can cause them to make inferior decisions.

Janis listed eight symptoms that show that concurrence seeking has led the group astray. The first two stem from overconfidence in the group's prowess. The next pair reflect the tunnel vision members use to view the problem. The final four are signs of strong conformity pressure within the group

1. Illusion of Invulnerability. Creates excessive optimism that encourages taking extreme risks

2. Belief in Inherent Morality of the Group. Members discount warnings and do not reconsider their assumptions.

3. Collective Rationalization. Members believe in the rightness of their cause and therefore ignore the ethical or moral consequences of their decisions.

4. Out-group Stereotypes. Negative views of “enemy” make effective responses to conflict seem unnecessary

5. Self-Censorship. Members are under pressure not to express arguments against any of the groups views.

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