Abstract

Task completion plans normally resemble best-case scenarios and yield overly optimistic predictions of completion times. The authors induced participants togenerate more pessimistic scenarios and examined completion predictions. Participants described apessimistic scenario f task completion either alone or with an optimistic scenario. Pessimistic scenarios did not affect predictions or accuracy and were consistently rated less plausible than optimistic scenarios (Experiments 1-3). Experiment 4 indepen-dently manipulated scenario plausibility and optimism. Plausibility moderated the impact of optimistic, but not pessimistic, scenarios. Experiment 5 supported a motivational explanation of the tendency to disregard pessimistic scenarios regardless of their plausibility. People took pessimistic scenarios into account when predicting someone lse's completion times. The authors conclude that pessimistic-scenario generation may not be an effective debiasing technique for personal predictions. At one time or another, many of us have smirked while passing a vacant lot with a weather-beaten sign announcing that a new supermarket will be "Opening Soon! " Such unwarranted optimism also pervades people's predictions of their task completion times. People tend to underestimate how long they will take to finish academic, household, and laboratory tasks (Buehler, Griffin, &