DIAG-3 · Diagnosis · Heuristic — strong prior, re-verify periodically
Twyman's law
The law
The more surprising a reported KPI movement, the more likely it is a measurement or pipeline artifact than a real market event.
Scope
Normal operating regimes; the prior inverts in genuinely volatile windows (crisis periods, accounts at the noise floor).
What this licenses you to do
Fixed triage order for any surprising delta: (1) measurement and definition audit, (2) mechanical decomposition, (3) market hypothesis last, and require confirmation from an independently instrumented source.
Evidence
Ehrenberg (1975); Kohavi, Tang & Xu (2020) catalogued extreme-result bugs.