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

@article{Buehler1994ExploringT,
  title={Exploring the "planning fallacy": Why people underestimate their task completion times.},
  author={Roger Buehler and Dale W. Griffin and Michael Ross},
  journal={Journal of Personality and Social Psychology},
  year={1994},
  volume={67},
  pages={366-381}
}
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… 

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