what the watch can't measure

My watch doesn’t know if I’m tired. It measures pace, heart rate, distance. Slowly, without noticing, I started trusting those numbers more than my own body. Before I had a GPS watch, I judged a run by the ache still in my legs after, by trying to slow my breathing enough to bring my heart rate down, by a guess at the distance, and the real number came from a course I already knew. Now the watch…