I started trend following (deep stop orders for fairly long hold periods, no shorts) in 2015. I knew I hadn’t hit a bear market or flash crash yet and that my system wouldn’t work anymore. I didn’t know how to define my bear market strategy in advance but when the time came, beginning in late February, I managed. Basically I stayed in cash until overall markets seemed to have bottomed, then bought deeply oversold things with decent fundamentals for holding indefinitely without stop orders. That has worked well, but now I need to start modulating back toward my original system, or at least start qualifying those indefinite durations. I mention my adjustments only as an example, understanding that most of you don't hold as long. What I hope to hear from others is how you adapt, modulate, and switch between trading systems.