A special case of choice shift is grouptbink (Janis 1982). Groupthink occurs when pressures to agree are so strong that they stifle critical thinking. For example, Diane Vaughan (1996) showed how groupthink contributed to the tragic 1986 explosion of the space shuttle Challenger. The engineers working on the Challenger all knew before the launch that the shuttle's O-rings probably would suffer some damage. But political pressures to launch the shuttle, coupled with a culture within NASA that rewarded risk taking, helped to create a situation in which the engi neers essentially convinced each other and themselves that the risk of O-ring fail ure was within acceptable limits. As this example illustrates, groupthink often re sults in bad decisions