Your worst-case guess is still an optimistic one

In 1994 Roger Buehler sat down with thirty-seven psychology students at Simon Fraser University and asked each of them for two dates to hand in their thesis: the normal one and the worst-case one, the date for when everything goes wrong. Only 30% met the first. Fewer than half met the second.

The average promised was 33.9 days; they took 55.5. You have given that second date yourself: the "Friday at the very latest" that turned into the following Thursday.

The failure has a specific cause. When you plan, you picture the work itself — writing, revising, handing it in — and you do not picture the flu, the meeting that runs over or the file that will not open. Buehler proved it from the other end: the students who were made to recall how long similar jobs had taken them came far closer.

So tomorrow, before you promise a date, do not estimate: look it up. Open your calendar, find the last time you did something similar, check how long it really took and give that number. If there is no precedent, take your estimate and multiply it by 1.6, which is exactly how far off the Simon Fraser students were.