In a series of experiments, researchers investigated people’s ability to accurately predict task completion times.
In their research, they discovered that people tended to make detailed plans for tasks based on optimistic future outcomes, rather than using past experiences to guide their predictions.
The planning fallacycan lead to poor planning for the future because it causes us to disregard practical estimated a task in favor of more optimistic and hopeful scenarios
See the full study here :
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. https://doi.org/10.1037/0022-3518.104.22.1686