What is the planning fallacy?

The planning fallacy is the tendency to underestimate how long our own tasks will take, even when we know that similar tasks took longer in the past. The term comes from the psychologists Daniel Kahneman and Amos Tversky, and later studies, such as Buehler, Griffin and Ross (1994), showed how reliably people fall into it.

Why it happens

When we estimate, we imagine the task going smoothly: no interruptions, no missing information, no tiredness. We focus on the plan for this task and forget our own track record with similar ones.

Why it matters

Plans built on optimistic estimates break early. One task runs over, the next starts late, and by the afternoon the whole day has slipped. With ADHD, where sensing time can be harder, the effect is often bigger.

How to plan around it

• Pad your estimates. Add half again to your first guess.
• Use your history. Look at how long similar tasks actually took last time.
• Leave empty time. Keep one unplanned block each day for whatever runs over.
• Compare estimate with actual. After a task, note the real time. Your estimates improve with feedback.

In Thendoo: give tasks an estimate, and focus sessions and the timer record the actual time, so you can compare estimated vs actual on each task and in Insights.