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Axtio
Psychology

The planning fallacy: why everything takes longer than you think

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Axtio Team
October 4, 2026 ยท 5 min read

"It'll take a couple of days." Two weeks later, it is still not done. Not because anyone was lazy, but because the estimate was made by a human brain, and human brains are reliably optimistic about their own work.

Psychologists Daniel Kahneman and Amos Tversky named this the planning fallacy in 1979: the tendency to underestimate the time, costs and risks of our own future actions, even when we know similar tasks took longer in the past.

The evidence

In a well-known 1994 study, Roger Buehler and colleagues asked students to estimate when they would finish their theses, including a "worst case" estimate. Most finished later than their own best guess, and a substantial share finished later than their worst-case estimate. The pattern has been found across many kinds of tasks, from homework to large public infrastructure projects.

Why it happens

  • We imagine the plan, not the interruptions. We picture the work going smoothly.
  • We ignore our own history. "This time will be different."
  • We forget the waiting. Estimates cover working time, not the days spent waiting for replies and approvals. See the handoff is the work.
  • Optimism feels good and is socially rewarded.

Practical fixes

Use the outside view. Instead of imagining this task, ask: how long did similar tasks actually take? Kahneman called this "reference class forecasting". Your own history is the best reference.

Count the waits. For any task that depends on someone else, add the realistic waiting time, not just the work.

Break work down. Smaller pieces are easier to estimate and reveal hidden work. See how to split a big project into actions.

Add a buffer, openly. Not padding hidden in every task, but a visible buffer at the end of the plan.

Review estimates afterwards. Compare estimated and actual. Over time, you learn your own bias.

Why visible waiting helps

Many plans fail not in the work but in the gaps between people. When waiting is tracked, you start to see how much of every project is spent in someone else's hands. In Axtio, actions in the Other column show how many days they have waited; looking back at a finished project, that history is a better guide to the next estimate than any optimistic guess. See the waiting-on-someone problem.

The kind takeaway

The planning fallacy is not a personal failing. It is a feature of how people think about the future. Plan around it rather than promising to be better next time. See next actions vs perfect planning.