Plexii glossary
Planning fallacy
The tendency to underestimate how long future work will take despite evidence from similar past tasks.
What it means
The tendency to underestimate how long your own tasks will take, even when similar tasks overran before. the term is usually credited to Kahneman and Tversky (1979) — The fix that follows: compare with your own past tasks rather than imagining this one.
The term is most useful as a shared description. It does not remove the need to look at the actual task, evidence or constraint in front of you.
A practical example
The last three reports took six hours, but the next is estimated at two because this time feels simpler.
Put it into practice
- Name the concrete situation before applying the label. Planning fallacy is useful only when it changes a choice, boundary or next action.
- Make the state visible: write the owner, time, source or stopping condition down instead of relying on memory.
- Review what happened. Keep the part that reduced ambiguity and change the part that added ceremony without helping the work.
How it relates to Plexii
: Your history shows your real time as a percentage of your estimates, and Predicted real time adjusts a new estimate by it (desk status time).