These people have put in years of base training before ever getting involved in competitive events. We have all read about their legendary daily runs to and from school during their childhood years. We cannot go back in time and commute to school by foot. However we can certainly take a more patient approach to our marathon training, realizing that every training period and the race which serves as it's ending is a significant building block in the ongoing process of marathon training. Rest is very important to the athlete in training.
Muscle tissue needs time to regenerate and strengthen.
Long runs should be followed by an easy day or two. Perhaps rest, crosstraining, or light running. Each of us is different in our needs, but some type of rest is necessary. Once you finish your marathon, stop and pat yourself on the back, and take a break. You've earned it, and more importantly your body needs it to recover.