Planning Fallacy
The Planning Fallacy is the tendency to underestimate the time, costs, and risks of future plans while overestimating their benefits, even when aware of past projects' tendency to run over. Described by Daniel Kahneman and Amos Tversky (1979), it is one of the most costly cognitive biases in project management, construction, software development, and government, and is best corrected using Reference Class Forecasting — anchoring estimates in the historical base rate of similar projects.