Exploring the 'planning fallacy': Why people underestimate their task completion times.
Buehler, Griffin and Ross tested three hypotheses about predictions of task completion time: that people underestimate their own completion times but not those of others, that they focus on plan-based scenarios rather than relevant past experience, and that their attributions reduce the relevance of past experience. Results supported all three. Predictions were too optimistic for a range of academic and nonacademic tasks, and think-aloud reports focused on future scenarios. The optimism disappeared when participants were told to connect relevant past experiences to their predictions, and observers overestimated others' completion times.
Buehler, Griffin and Ross tested three hypotheses about predictions of task completion time: that people underestimate their own completion times but not those of others, that they focus on plan-based scenarios rather than relevant past experience, and that their attributions reduce the relevance of past experience. Results supported all three. Predictions were too optimistic for a range of academic and nonacademic tasks, and think-aloud reports focused on future scenarios. The optimism disappeared when participants were told to connect relevant past experiences to their predictions, and observers overestimated others' completion times.
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Buehler, R., Griffin, D., & Ross, M. (1994). Exploring the planning fallacy: Why people underestimate their task completion times. Journal of Personality and Social Psychology, 67(3), 366-381. doi:10.1037/0022-3514.67.3.366