The planning fallacy is a phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed. This phenomenon sometimes occurs regardless of the individual's knowledge that past tasks of a similar nature have taken longer to complete than generally planned.[1][2][3] The bias affects predictions only about one's own tasks. On the other hand, when outside observers predict task completion times, they tend to exhibit a pessimistic bias, overestimating the time needed.[4][5] The planning fallacy involves estimates of task completion times more optimistic than those encountered in similar projects in the past.
Daniel Kahneman who, along with Amos Tversky, proposed the fallacy
The planning fallacy was first proposed by Daniel Kahneman and Amos Tversky in 1979.[6][7] In 2003, Lovallo and Kahneman proposed an expanded definition as the tendency to underestimate the time, costs, and risks of future actions and at the same time overestimate the benefits of the same actions. According to this definition, the planning fallacy results in not only time overruns, but also cost overruns and benefit shortfalls.[8]
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^Kruger, Justin; Evans, Matt (15 October 2003). "If you don't want to be late, enumerate: Unpacking Reduces the Planning Fallacy". Journal of Experimental Social Psychology. 40 (5): 586–598. doi:10.1016/j.jesp.2003.11.001.
^Koole, Sander; Van't Spijker, Mascha (2000). "Overcoming the planning fallacy through willpower: Effects of implementation intentions on actual and predicted task-completion times" (PDF). European Journal of Social Psychology. 30 (6): 873–888. doi:10.1002/1099-0992(200011/12)30:6<873::AID-EJSP22>3.0.CO;2-U. hdl:1871/17588. Archived from the original (PDF) on 2019-11-29.
^Cite error: The named reference buehlerHandB was invoked but never defined (see the help page).
^Cite error: The named reference abouttime was invoked but never defined (see the help page).
^Pezzo, Mark V.; Litman, Jordan A.; Pezzo, Stephanie P. (2006). "On the distinction between yuppies and hippies: Individual differences in prediction biases for planning future tasks". Personality and Individual Differences. 41 (7): 1359–1371. doi:10.1016/j.paid.2006.03.029. ISSN 0191-8869.
^Kahneman, Daniel; Tversky, Amos (1977). "Intuitive prediction: Biases and corrective procedures" (PDF). Archived (PDF) from the original on September 8, 2013. {{cite journal}}: Cite journal requires |journal= (help) Decision Research Technical Report PTR-1042-77-6. In Kahneman, Daniel; Tversky, Amos (1982). "Intuitive prediction: Biases and corrective procedures". In Kahneman, Daniel; Slovic, Paul; Tversky, Amos (eds.). Judgment Under Uncertainty: Heuristics and Biases. Vol. 185. pp. 414–421. doi:10.1017/CBO9780511809477.031. ISBN 978-0511809477. PMID 17835457. {{cite book}}: |journal= ignored (help)
^Lovallo, Dan; Kahneman, Daniel (July 2003). "Delusions of Success: How Optimism Undermines Executives' Decisions". Harvard Business Review. 81 (7): 56–63. PMID 12858711.
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