Planning Fallacy

Kahneman & Tversky (1994) - Planning Fallacy Study | Wikipedia - Planning Fallacy

Planning Fallacy describes the tendency to underestimate time, costs, and risks of future actions while simultaneously overestimating their benefits. Research by Kahneman and Tversky (1979) and Buehler demonstrated this bias empirically: In a study of 37 psychology students estimating thesis completion time, only 13% finished by their 50% probability estimate, only 19% by their 75% estimate, and only 45% by their 99% estimate. The bias stems from wishful thinking, self-serving attribution of delays to external factors, and taking an “inside view” focused on specific task details rather than historical data from similar past projects.