The planning fallacy
We nearly always underestimate how long things will take, even when we have been wrong before. There is a fix.
You say a task will take an hour, and it takes three. You are sure you will finish the project by Friday, and it runs into the following week. If this sounds familiar, you are in good company.
The psychologists Daniel Kahneman and Amos Tversky gave this tendency a name in 1979: the planning fallacy. People make predictions about their own projects that are far too optimistic, even when they know similar projects ran late.
Why it happens#
When we plan, we imagine the task going smoothly. We picture the steps, in order, with no surprises. We rarely picture the phone call that eats the afternoon, the missing file or the day we feel ill.
We also tend to think our case is special. Other people's projects overrun, but ours will be fine.
How to fix it#
There are some simple habits that help:
- Look at the past. How long did the last similar task actually take? Use that number, not your hope.
- Add a buffer. A common approach is to add a third or a half to your first estimate.
- Break it into parts. Estimating small pieces is more accurate than guessing a whole.
- Ask someone else. An outside view tends to be more realistic than your own.
Track your time#
For a week or two, write down how long things take. You will probably find that the same kinds of tasks take roughly the same time. Those numbers are valuable. They turn a hunch into something you can plan with.
An easy example#
Say you think a report will take two hours. Last time a similar one took four. Plan for four, and you will either be on time or pleasantly early. Plan for two, and you will be stressed on the day.
The planning fallacy is not a flaw you can stop having. It is a bias to plan around, and a little humility goes a long way.