Halfway through building my audio synthesis engine, I hit a specific wall. Something sounded wrong. Not broken — just slightly off in a way I couldn't immediately point at. I asked AI to review the logic. It told me everything looked correct. I almost moved on. I didn't. I kept pulling at it. Turned out the logic was wrong in a way that only becomes obvious when you understand what the code is supposed to be physically modelling. No test was going to catch it. AI had no way to hear what I was hearing. And if I'd trusted the output over my instinct, the whole synthesis engine would have been quietly wrong from that point forward. That experience shaped how I finished the build. But I'm getting ahead of myself. What I was actually building I've been tracking HRV and sleep for a couple of years. Every morning I wake up to five numbers: heart rate variability, resting heart rate, deep sleep %, REM %, stress score. I got pretty good at reading them.…