Some people who run for exercise discover that the fear of quitting - not the fear of running painfully, but of quitting - becomes so severe that they are tempted to quit to get rid of the fear. Once they've run the course the mental agony is gone and the physical agony bearable; so they sometimes treat themselves at the end to a little extra when, anxiety gone and nothing at stake, they can at last run for the fun of it.
Made me think a little bit. Interesting.