You'll underestimate how long a task takes, even knowing this about yourself

Daniel Kahneman and Amos Tversky named this tendency to predict unrealistically short timelines for our own projects, even while knowing similar tasks have run late before. The Sydney Opera House was budgeted at $7 million and finished a decade late at over $100 million — a textbook case cited ever since.

— Daniel Kahneman, Amos Tversky, Intuitive Prediction: Biases and Corrective Procedures — TIMS Studies in Management Science, 1979