# 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.

## 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 (/help/desk-status-time).

## Sources

- [Buehler, Griffin and Ross, 1994](https://doi.org/10.1037/0022-3514.67.3.366)