You reckoned 34 days and took 55: it was not bad luck

In 1994, three psychologists at Simon Fraser University in Vancouver asked a group of students when they would finish their final-year thesis. The average forecast was 33.9 days. The real average was 55.5.

Roger Buehler, Dale Griffin and Michael Ross named it the planning fallacy: the optimistic sum your head does when it plans a specific task of its own. The good part comes next. The same students were asked for a second number, the worst imaginable scenario, the "if everything goes as badly as it possibly could" one. They said 48.6 days. They missed that too: reality ate a week more than their own catastrophe.

It was not that they could not count. When those students estimated a classmate's deadline, their forecasts stretched out. Optimism spikes when the plan is yours, because you build it looking at the ideal script — the one with no flu, no weddings, no boss with an emergency — instead of looking at your own record.

Hence the fix, and it fits on one line: don't estimate, remember. Before you say "by Thursday", find the last time you did something similar, look at how long it actually took and use that number, even if it embarrasses you. If you never wrote it down, write down today's.