I almost quit this year’s New York City Half Marathon. The moment is seared into my brain. I’d been running for nearly two hours in freezing temperatures, straight into the wind. The Apple Watch Ultra on my left wrist buzzed to tell me I’d just passed mile nine. On my right wrist, the Garmin Forerunner 265S said I’d only run 8.55 miles. A short-ish distance ahead, I could see the official mile nine marker. I had no idea which distance was “true.” It didn’t matter, though. All I wanted was to beat last year’s time, even by just one millisecond….