Markets don't behave the same way all the time — they cycle through volatility regimes. A low-volatility regime is calm, often trending or grinding, with small ranges. A high-volatility regime is turbulent, with large ranges, gaps, and violent reversals. The two are almost different markets, and a strategy built for one can fail badly in the other.
Why regime governs everything
A mean-reversion strategy that fades extremes works in a calm, range-bound regime and gets destroyed in a trending, high-vol breakout. A trend-following breakout strategy is the reverse. The same signal, the same setup, produces opposite results depending on the regime. This is why identifying the regime is often more important than the entry logic itself.
How regimes transition
Volatility clusters and is mean-reverting: calm periods tend to persist, then transition — often abruptly — into turbulent ones, and vice versa. A long volatility squeeze frequently precedes an expansion; a fear spike eventually exhausts and reverts. The dangerous moments are the transitions, when a strategy tuned to the old regime is still running as the new one begins.
Most blown-up strategies weren't wrong. They were right — for a regime that had already ended.
Reading it
Tools like the VIX, term structure, VVIX, ATR, and ADX all help gauge the current regime. A robust system doesn't just have signals — it has an awareness of which regime it's in and adapts (or stands down) accordingly. Detecting the regime before applying a strategy built for the other one is one of the quietest, most durable edges in systematic trading.