Because nothing is harder than running the mile. Nothing. Not the 100 meters or the 10K or even the marathon. The mile, or its metric equivalent, the 1,500 meters, demands the ultimate combination of speed and strength. In training, I run sprints till I drop and I also cover distances as far as 20 miles. I train in pain because I race in pain and if you can’t tolerate pain you may as well quit. You won’t be a miler.