ABSTRACT: This article applies the model of decisionmaking to the planning for Operation Market Garden in late 1944. It shows especially strong parallels between decision-making in the Market Garden case, and those of the Bay of Pigs, Vietnam, and the Challenger shuttle disaster. ********** In 1982, social psychologist Irving Janis--heir to a long line of others who had shown how social pressures and the power of the situation can combine to make us do things we never dreamed we would--published the second edition of his book Groupthink. (1) Originally published a decade earlier, the book articulated the groupthink hypothesis, arguing certain tight-knit groups were especially prone to making policy errors. Some groups induce conformity or groupthink, a process through which a group reaches a hasty or premature consensus and then becomes effectively closed to outside ideas. In Janis's model, the rationality of decisions is distorted by dysfunctional group and social forces because members come to prize unanimity and agreement over considering all courses of action rationally. (2) Janis referred to this tendency as a concurrence-seeking. (3) Once the group has reached its decision, that decision cannot be revisited or reconsidered. Dissenters are progressively excluded or shunted aside altogether. Self-censorship occurs as those who disagree with the chosen course of action remain silent, often because they think changing the minds of others is hopeless. Furthermore, mindguards are apt to appear, individuals who take it upon themselves to police the decision taken and to dissuade dissenters from rocking the boat. This action can sometimes lead to the removal of a determined dissenter from the group altogether, or else to the effective silencing of the individual. Janis discussed a number of the symptoms of as well as the antecedent conditions that could produce it. (4) These conditions encourage the symptoms but do not necessarily produce them. Of these, an especially important factor is group cohesiveness, where a clubbish atmosphere develops between the members. Often this atmosphere occurs when the decision-makers have spent a great deal of time with one another or begin to socialize together. During the Kennedy/Johnson era, for example, many members of the administration stayed in the same posts for several years and came to know one another very well. While cohesiveness is critical to many teams--including military ones --this trait is a double-edged sword; a group in which members become overly familiar with one another can come to think alike and can fail to question each other's assumptions. Decisions regarding Vietnam, for instance, were made by a collection of like-minded individuals who agreed on aspects of foreign policy, and cultivated an atmosphere of consensus. Other pre-conditions include a history of failure, stress induced by time pressure, and overly directive leadership of the type that allows no disagreement. Margaret Thatcher, for instance, was known for arriving at meetings already having decided what she wanted, stating her position upfront and then effectively challenging others to disagree with her. There is also what Janis calls suave leadership, where a leader induces docility and a false sense of complacency. (5) The presence of a charismatic president in 1961 during the disastrous Bay of Pigs episode appeared to reinforce the idea that the plan was in fact a good one. But he allowed the CIA to monopolize the discussion, failing to encourage his advisers to ask tough questions that might have exposed the plan's flaws before it went into effect. The symptoms of groupthink, similarly, take on disturbingly common forms. They include the following: * Illusions of invulnerability. The group comes to believe it cannot lose. As Janis sees it, the new Kennedy officials who came to office in 1961 were laboring under an illusion of invulnerability, believing they were winners. …