Over the past two years, a simple but baffling request has preceded most of my encounters with medical professionals: “Rate your pain on a scale of zero to 10.” I trained as a physician and have asked patients the very same question thousands of times, so I think hard about how to quantify the sum of the sore hips, the prickly thighs, and the numbing, itchy pain near my left shoulder blade. I pause and then, mostly arbitrarily, choose a number. “Three or four?” I venture, knowing the real answer is long, complicated, and not measurable in this one-dimensional way. Pain is a squirrely thing. It…