What distinguishes those of us at the starting line from those of us on the couch is that we learn through running to take what the days gives us, what our body will allow us, and what our will can tolerate.
You don't run against a bloody stop watch, do you hear? A runner runs against himself, against the best that's in him. Not against a dead thing of wheels and pulleys. That's the way to be great, running against yourself. Against all the rotten mess in the world. Against God, if you're good enough.