The planning fallacy refers to the tendency to underestimate task-completion times. Real-life examples in public policy may include the construction of the Sydney Opera House and the Big Dig, both of which ran many years past their planned schedule.

In one study, 37 students were asked to estimate the completion times for their senior theses . The average estimate was 33.9 days. Only about 30% of the students were able to complete their thesis in the amount of time they predicted, and the average actual completion time was 55.5 days.

Some have attempted to explain the planning fallacy in terms of impression management theory.

Compare to procrastination.

See also

• list of cognitive biases
• wishful thinking.

References

• 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, 366-381.
• Buehler, R., Griffin, D., & Ross, M. (2002). Inside the planning fallacy: The causes and consequences of optimistic time predictions. In T. Gilovich, D. Griffin, & D. Kahneman (Eds.), Heuristics and biases: The psychology of intuitive judgment, 250-270. Cambridge, UK: Cambridge University Press.