The Planning Fallacy Affects Everyone, Including Experts

People consistently underestimate how long tasks will take — even when they've done similar tasks before. This is the planning fallacy, first identified by Daniel Kahneman and Amos Tversky in 1979. The fix isn't optimism or pessimism: it's using "reference class forecasting" — looking at how long similar projects actually took for other people.

Source: Thinking, Fast and Slow — Daniel Kahneman