Classify evidence by diagnostic value before updating…
When new evidence arrives, classify it by diagnostic value before updating—ask whether you'd see this evidence regardless of belief truth versus only if belief were true/false.
When This Fires
- Interpreting customer behavior, market signals, or team dynamics
- Evaluating whether new data supports or undermines a hypothesis
- Deciding how much to update a project estimate based on recent results
- Any time new information arrives and you're about to change your plan
Common Failure Mode
Counting confirmations without checking diagnostic value. Every piece of evidence that's consistent with your belief feels like support — but most evidence is consistent with multiple hypotheses. Seeing a long line at a restaurant is consistent with "the food is great" and also with "it's the only restaurant nearby" and "they're slow." The observation doesn't help you discriminate between these explanations, so it shouldn't move your estimate much.
The Protocol
When new evidence arrives: (1) Ask: "Would I see this evidence if my belief were true AND if my belief were false?" (2) If yes to both → low-diagnostic. Barely update. (3) If you'd see it mainly when your belief is true (or mainly when false) → high-diagnostic. Update significantly. (4) Adjust the size of your update to the diagnostic value, not to the emotional impact of the evidence.