This is a Lexicon entry: the mechanism, when it shows up, and the countermeasure. The full correction, with real-world cases and the audit prompt, hasn't been written yet.
Definition
The tendency to underestimate the amount of time needed to complete a future task. Almost every major project - software, construction, government initiatives - takes longer and costs more than predicted.
When it shows up
Estimating how long a project will take, how much a renovation will cost, how long a government program will last. Any commitment to future completion. Modern context: A product roadmap is built with three-week sprint estimates for each feature. The historical completion rate for similar sprints at the organisation is 60% of estimated scope. The roadmap is presented to stakeholders as a committed plan, not a probability distribution. High-stakes instance: Software development - the average enterprise software project runs 45% over budget and 7% over schedule; projects using detailed upfront estimates perform no better than those using reference class forecasting and substantially worse than those using iterative commitment. Failure mode: Estimates are generated by visualizing the successful path (the 'happy path') and summing its durations. The probability-weighted distribution of obstacles, setbacks and delays is absent from the mental model so the estimate is a best-case prediction. Estimated cost: High - often irreversible where this bias dominates unchecked decisions.
Failure mode
Estimates are generated by visualizing the successful path (the 'happy path') and summing its durations. The probability-weighted distribution of obstacles, setbacks and delays is absent from the mental model so the estimate is a best-case prediction.
Countermeasure
Look up what actually happened to the last ten comparable projects. Use the distribution of their actual durations/costs, not your plan's steps, as the estimate. When correction costs more than the bias: Morale and commitment benefit from ambitious targets. Teams that plan to the reference class become anchored to base rates and may underperform what motivated effort could achieve. Apply reference class forecasting for budget and resource allocation; allow optimistic planning for goal-setting and motivation.
Related traps
Also connected in the map9 more, locked
Also revealed
Entry #75 of 631 in The Lexicon · see the full Lexicon