You don't run 26 miles at five minutes a mile on good looks and a secret recipe.
Why couldn't Pheidippides have died at 20 miles?
Right now, after having had back surgery, I am finally back to running again.
Running with others can help get you out when you might otherwise blow it off.
Experience has taught me how important it is to just keep going, focusing on running fast and relaxed. Eventually it passes and the flow returns. It's part of racing.
A good athlete always mentally replays a competition over and over, even in victory, to see what might be done to improve the performance the next time.