Estimate time and effort with an outside view instead of relying only on the current plan.
Open situation →Reasoning Practice · Intermediate
A detailed plan with no outside view
A team has a detailed task plan for a data migration. It predicts 40 days, but nobody has checked how long similar migrations actually took.
Your decision
Which evidence should be added first?
Show the best first move
B. A reference class of comparable completed migrations and their actual duration range.
Why this move helps
More inside detail can improve execution planning without correcting the baseline. Reference-class forecasting tests the plan against completed cases.
Evidence still missing
- Durations of comparable completed migrations.
- Reasons this project differs from the reference class.
- The distribution, not only the best or worst example.
Evidence note
Planning fallacy is a plausible lens when the estimate relies mainly on the inside plan. A poor reference class can also mislead, so comparability must be explained.
Next action
Set an outside-view range first, then document any evidence-based adjustment.
Best first lens
Planning Fallacy
Use the lens to ask a better question. It does not prove that a person or team has a cognitive bias.
Other defensible lenses
The situation may have more than one explanation.
Continue the path
Situation → skill → technique → action.
You can produce forecasts that are easier to challenge, compare and learn from later.
Build this skill →Use outcomes from comparable completed cases before refining an inside-view plan.
Run the technique →