Planning Fallacy
A phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed.
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Origin
Proposed by Daniel Kahneman and Amos Tversky in their 1979 paper 'Intuitive Prediction: Biases and Corrective Procedures,' from their broader research into cognitive biases at the Hebrew University of Jerusalem. They attributed the bias to an 'inside view' — people focus on the specifics of a task rather than drawing on how long similar tasks have actually taken.
Updated February 22, 2026