Exploring the "planning fallacy": Why people underestimate their task completion times.

TLDR

The study tested whether people underestimate their own task completion times, rely on plan-based scenarios rather than past experiences, and attribute past prediction failures to external factors. Results confirmed all hypotheses: participants were overly optimistic about their own tasks, focused on future scenarios, reduced bias by recalling past experiences, overestimated others’ times, and attributed failures to external, transient factors.

Abstract

This study tested 3 main hypotheses concerning people's predictions of task completion times: (a) People underestimate their own but not others' completion times, (b) people focus on plan-based scenarios rather than on relevant past experiences while generating their predictions, and (c) people's attributions diminish the relevance of past experiences. Results supported each hypothesis. Ss' predictions of their completion times were too optimistic for a variety of academic and nonacademic tasks. Think-aloud procedures revealed that Ss focused primarily on future scenarios when predicting their completion times. In Study 4, the optimistic bias was eliminated for Ss instructed to connect relevant past experiences with their predictions. In Studies 3 and 4, Ss attributed their past prediction failures to relatively external, transient, and specific factors. In Study 5, observer Ss overestimated others' completion times and made greater use of relevant past experiences.