D·02
Decisions & Judgment
The Planning Fallacy
Your estimate of how long this will take is an estimate of the best case, and you know it is not the best case.
- Evidence
- proven
- Topic
- Decisions
- Things to do
- 3
- Read
- 1 min
provenHow strong is the evidence?
Tested again and again, by different people, and it keeps coming out the same. You can lean on this.
- Buehler, Griffin & Ross, 1994
- Kahneman & Tversky, 1979
Why it works
We plan by imagining the sequence of steps, and the imagined sequence never includes the interruptions that actually consumed last time.
What to do about it
- Do not re-estimate. Look up how long the last three similar things actually took.
- Ask someone who is not doing the work for their estimate. Observers are better calibrated.
- Write the estimate down with a date, so you find out whether you're biased and by how much.
Where people go wrong
Adding a buffer to a fantasy. A 50% buffer on a wrong method is still the wrong method.
Read next
- Start From the Base RateAsk what usually happens to cases like this one before you consider what is special about this one.proven
- The Pre-MortemBefore committing, assume it is eighteen months later and the project has failed. Write the story of why.solid
- It Will Matter Less Than You ThinkWe badly overestimate how long any outcome — good or bad — will affect our happiness.solid
- Sunk Costs Are Not CostsMoney and years already spent are gone whatever you now decide. The only question is forward value.proven