Planning fallacy
The planning fallacy is underestimating how long a task will take, and often how much it will cost, even when similar past tasks ran over. We picture the smooth, best-case path and forget the delays.
In everyday life
A couple budgets three months for a kitchen remodel, and it ends up taking most of a year and costing far more.
You tell your boss the report will be ready by Friday, just as you did for the last five reports, each of which took until the following Wednesday.
Why your mind does this
Imagining the past and the future is hard, so the brain uses the present as a template. Assuming things will stay roughly as they are now is a quick and usually workable guide. Making sense of events after the fact also helps us learn lessons and feel in control.
How to spot it
Ask how long similar tasks actually took you in the past, and compare that with your current estimate.
How to counter it
Base your estimate on the track record of similar past projects, then add a buffer.
Habits that catch it
- Start from the base rate
Ask how things like this usually turn out before you look at what makes this case special.
Same family: Projecting ourselves
SourcesBuehler et al. (1994)·Wikipedia