Index

Cognitive Biases

Planning Fallacy

A bias where people predict tasks will take less time and resources than they actually require.

Planning fallacy causes chronic schedule slip by over-weighting optimistic scenarios and underweighting friction.

Core question

What do similar projects usually cost in time and effort, not what we hope this one will cost?

Example

A redesign estimated at three weeks takes two months once QA, migration edge cases, and stakeholder cycles are included.

How to apply

  1. 1.Use reference class forecasting from past similar work.
  2. 2.Break projects into smaller estimates with confidence ranges.
  3. 3.Add explicit contingency for uncertainty and rework.
  4. 4.Review estimates with someone outside the project team.

Pitfalls

  • ·Treating best-case timelines as expected timelines.
  • ·Ignoring coordination and approval delays.
  • ·Believing motivation can eliminate structural complexity.

Questions

What is a planning fallacy example in software?

Teams often estimate coding time but forget integration testing, bug triage, and release coordination.

What is the best way to counter planning fallacy?

Reference class forecasting is strongest: compare against actual timelines from similar completed work.

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