Runner, Know Thyself

The following is from a book by Frank Shorter, the 1972 Olympic Marathon gold medalist.It's called Olympic Gold: A Runner's Life and Times.
Much is to be learned from what Frank has to say. Most have forgotten that decades ago he led an effort to eliminate drug use from distance running competition, a noble endeavor indeed. Ironically,the '76 Olympic marathon champion Waldemar Ciepinski,whom Shorter finished less than a minute behind for the silver, was widely believed to be a drug cheat(since confirmed). Nothing ruins a sport's credibility more than illegal drug use. If you doubt that, then take a look at what it's done to baseball's homerun record for starters.
But I digress. Here Frank gives an insight into something that can't be stressed enough,especially if you desire racing success:
 "You have to know your body. It's part of the beauty of the training process,and once you've determined how much your body (and mind) can take, you can then begin to reach your potential. As intensely as I've trained over the years,I never felt I was training too hard. I always felt I had a little more to give. I think I've grown to know my body and exactly how it reacts to running. I can detect subtle changes in the way I run and feel, which better enables me to gauge the effort I put into running and the training effect I might derive. I know when I'm fit,and why; I know when I'm not, and why."
Again,serious training involves more than just lacing on the shoes and doing the workout.