Planning Fallacy

A well-documented cognitive bias, identified by Kahneman and Tversky and elaborated by Buehler and colleagues, in which people systematically underestimate how long their own tasks will take and overestimate how much they can finish, even when they have direct evidence that similar past tasks took longer. The bias is amplified by optimism, by focusing on the inside view of a specific plan rather than the base rate of comparable projects, and by a desire to please others. For people with ADHD, the planning fallacy compounds with weak time perception, working-memory load, and emotional avoidance, making to-do lists chronically over-ambitious. Productivity tools, calendars, and AI assistants can mitigate the fallacy by surfacing historical completion times, prompting reference-class comparisons, and adding deliberate buffers.