When possible, take the outside view. Avoid estimating the time for a project by adding time estimates for sub-tasks; instead, look for previously completelycompleted projects of similar type and scale, and base the estimate on how long those other projects took.
"It always takes longer than you expect, even when you take into account Hofstadter's Law."
-- Hofstadter's Law, from Gödel, Escher, Bach: An Eternal Golden Braid
The bias also seems to be related to taking an "inside", detail-oriented view of the project to be planned; studies show that the more detailed a plan is, the more optimisticlyoptimistically inaccurate it is likely to be.
When possible, avoidtake the outside view. Avoid estimating the time for a project by adding time estimates for sub-tasks; instead, look for previously completely projects of similar type and scale, and base the estimate on how long those other projects took.
AThe Planing Fallacy is a common cognitive bias resulting in predicting absurdly short timeframes for planned projects, famously observed with, among other projects, the Sydney Opera House, completed ten years late and a hundred million dollars overbudget.