I remember the last time I went skiing in Colorado. The snow was perfect, the sky a brilliant blue, and I was exhilarated by the crisp mountain air. On one of my early runs, as I sped toward the lift, I made a sharp stop. But then, in an awkward fall, I used my arms to protect my face from the hard-packed snow. The impact was so intense that I felt my right shoulder pop out of its socket.

Determined not to waste the perfect skiing day, I lay on the snow, grabbed my right arm, pulled it out, and guided my shoulder back into its socket. Remarkably, it worked. I met my friends a few minutes later, kept quiet about my injury, and continued skiing. That night, the pain was excruciating, making sleep nearly impossible.