Optimism Bias in Project Decisions
Check optimism bias by starting with outcomes from comparable past projects before adjusting for the current plan's specific advantages.
Example: a six-week migration estimate
The task plan totals six weeks, while the last eight migrations took seven to thirteen. Two new automation steps justify a modest reduction, not ignoring the entire reference class. The commitment is made against a range.
Plans describe intentions, not frequencies
A detailed schedule feels persuasive because every step has an owner. It does not show how often similar work encountered rework, dependency delays, or scope change. The outside view supplies a starting rate before the current story modifies it.
Use an outside-view forecast
- Define a comparable project class.
- Record typical time and cost ranges.
- List only case-specific differences with evidence.
- Keep a contingency tied to the remaining spread.
Pessimism is not the cure
Adding an arbitrary buffer hides the reasoning. Use observed variation and explicit adjustments so the forecast can improve after the outcome.
The decision rule
What to record before acting
Begin with comparable outcomes, then adjust only for differences that have a credible effect and evidence.
Apply the rule in context with compare downside and upside ranges. Keep the evidence and assumptions with the decision so an outcome review can distinguish reasoning from luck.
Continue within decision psychology
Choice-Supportive Bias After a Decision
Prevent choice-supportive bias by preserving the original alternatives, expectations, and evidence before learning the outcome.
Choice-Supportive Bias After a DecisionThe Affect Heuristic in Decisions
Use an emotional reaction as a clue to a valued consequence, then verify the belief beneath it with the same standard used for both options.
The Affect Heuristic in Decisions