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Exploring the "Planning Fallacy": Why People Underestimate Their Task Completion Times

Authors:
Roger Buehler at Wilfrid Laurier University
Roger Buehler
Dale Wesley Griffin at University of British Columbia
Dale Wesley Griffin
Michael Ross at University of Waterloo
Michael Ross
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Abstract

Tested 3 hypotheses concerning people's predictions of task completion times: (1) people underestimate their own but not others' completion times, (2) people focus on plan-based scenarios rather than on relevant past experiences while generating their predictions, and (3) people's attributions diminish the relevance of past experiences. Five studies were conducted with a total of 465 undergraduates. Results support 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. The optimistic bias was eliminated for Ss instructed to connect relevant past experiences with their predictions. Ss attributed their past prediction failures to external, transient, and specific factors. Observer Ss overestimated others' completion times and made greater use of relevant past experiences. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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... • and the Planning Fallacy, the tendency for project forecasters and managers to overpromise and under-deliver (Buehler et al., 1994;Lovallo & Kahneman, 2003;Flyvbjerg, 2006;Lovallo et al., 2023). ...
... 2-2) observed: "Scientists and writers, for example, are notoriously prone to underestimate the time required to complete a project, even when they have considerable experience of past failures to live up to planned schedules." Project leaders behave as if their assigned project will go as planned even though historical evidence suggests that most projects from a relevant comparison set fall short of their planned targets (Buehler et al., 1994). Kahneman and Tversky (1977, pp. ...
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... Yet, empirical evidence showing that people invest more effort after being exposed to or comparing themselves with a downward comparison standard is scarce. Generally, people hold positive illusions about their future and are overly optimistic about their chances of success and their health (Buehler et al., 1994;Taylor et al., 2000). Because of this optimism, they might not fear becoming like the negative exemplar, rendering the standard irrelevant. ...
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