Planning Fallacy
We underestimate how long tasks will take and how much they will cost.
The planning fallacy is a phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed. This phenomenon sometimes occurs regardless of the individual's knowledge that past tasks of a similar nature have taken longer than generally planned. Kahneman and Tversky first described the effect in 1977.
What it looks like in the wild.
- Everyday life Home Renovation Home renovations almost universally exceed their original time and budget estimates, yet homeowners making new estimates continue to show the same optimism.
- Everyday life Software Development Software projects are notoriously late — the planning fallacy is so common in software that Hofstadter's Law states: 'It always takes longer than you expect, even when you account for Hofstadter's Law.'
Recognising a definition is not the same skill as spotting it.
Two scenarios from the app, with distractors drawn from the same family of biases — which is what makes them hard.
The author promises her editor the final manuscript in a month. She's only accounted for the time to type up her notes, not the extensive rewriting and fact-checking required.
Elena signs up for a 5K race happening in six weeks. She hasn't run in years but believes she can get into race-ready shape by running twice a week.
Biases rarely arrive alone.
Understand more. Assume less.
188 biases, 18,869 scenarios, and a record of how you actually decide.
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