Why Are We Sometimes Terrible at Guessing Time?

Ten minutes seems like plenty of time until the thing you are doing takes twenty-five. Part of the problem is that we often estimate time using what we think something will be like. We forget the setup, the parts that take longer than expected, getting stuck, finding what we need and all the little interruptions along the way. That is why actually timing yourself gives you something useful: evidence from your own experience.

Suppose you think a homework assignment will take 15 minutes and it regularly takes 30. That isn't a reason to become annoyed with yourself. It is useful information. Next time you have something similar, you have a much better starting point for your plan. You don't need to predict every minute perfectly. The closer your plans get to real life, the fewer times schoolwork unexpectedly eats into the time you thought was yours.