People planning a task reliably underestimate how long it will take, and the underestimate survives experience. A person who has been late on the last five projects will confidently predict an on-time finish for the sixth. This is one of the most robust findings in the study of judgement, and the mechanism is more specific than general optimism.
When estimating, people construct a scenario: they imagine the task going as intended, step by step, and time the scenario. The imagined version contains no illness, no waiting for a reply, no realising halfway through that the data is in the wrong format. Each of those is individually unlikely, which is exactly why none appears in the imagined run, and collectively they are near certain.
The correction that works is unglamorous and does not involve thinking harder. It is to ignore the plan and look at the record: how long did similar tasks actually take, including the ones that went badly? This is called taking the outside view, and the striking thing is that people resist it even when the record is available, because the record feels unfair. This time is different, and this time is always different, and the record already contains every previous time that was different.
For a student the version is small enough to test. Before estimating how long an essay will take, look at how long the last three actually took from first sentence to final full stop. The number will be larger than the estimate you were about to make, and it will be closer.
Vocabulary in this text
- experience /ɪkˈspɪɹiəns/ — knowledge from doing something, or an event you live through
- robust /ɹoʊˈbʌst/ — strong enough to keep working in difficult conditions
- mechanism /ˈmɛkəˌnɪzəm/ — the way a process or machine works
- specific /spəˈsɪfɪk/ — exact and clearly stated
- estimate /ˈɛstəmət/ — to say approximately how much or how many
- construct /kənstɹˈʌkt/ — an idea defined by researchers in order to study it
- imagine /ˌɪˈmædʒən/ — to form a picture in your mind
- realise /ɹˈiəˌlaɪz/ — to understand something for the first time
- appear /əˈpɪɹ/ — to become possible to see, or to seem
- similar /ˈsɪməlɚ/ — almost the same