Often when you long for something--when you dream of it for years, picture it, yearn for it--it becomes so idealized in your mind that when it actually happens, it can't possibly live up to your imagined version. For eight years I have been deprived, by my doctor's orders, of the opportunity to run more than six miles. My running regimen during those years was sporadic (often limited to the summer months), and rarely did I run over three miles. But throughout those years, with an intensity and frequency that slowly built to a sense of urgency, I yearned to run long. I pined for those chilly Kellogg mornings when I got up at 4:30 to beat the heat, so I could get in my 10, 12, even 20-miler. I missed the meditative and restorative power of running for an hour or two or three. Still, I could not help but wonder if I had romanticized this experience. Was I just longing for it because I had been told I could not have it? What if a long run turned out to be just long and hard and...