Kept getting chopped up in US500 — then I checked the Efficiency Ratio. Here's what 68K bars show.

I was running the same momentum setup across all conditions. Some months I'd crush it, others I'd give back 3 months of gains in 2 weeks. Blamed "market manipulation" until I actually measured what market I was trading in. **What I found:** Markets are in choppy/ranging mode 63% of the time. Not 30%. Not 40%. Two-thirds of your trades happen in conditions that shred trend strategies. **The test:** Same entry signals. Same exits. Only difference: position sizing based on Efficiency Ratio regime. Always momentum: 0.30x return (-70%), Sharpe -0.51, drawdown -71% ER Regime-Aware: 2.78x return (+178%), Sharpe 0.68, drawdown -20% **The rules (simple):** * ER > 0.6 + ER50 > 0.5 → Full momentum size * ER < 0.3 -> Mean reversion mode or sit out * Between 0.4-0.7 -> Half size, careful **The kicker:** Strong trends (ER > 0.7) only happen 0.5% of the time in my data. I was betting on black swans with full size. Now I know when I'm fishing in the wrong pond. **Caveat:** Doesn't work everywhere. Tested on EUR/USD (works) and Gold (fails). Asset matters. **Question:** Do you adapt position size to market regime? Or run the same strategy regardless of conditions?