At some point, the marathon will move beyond the physical capacity of your body or training. You will enter a really tough, hard-to-define area where your ability to continue moving is what separates you from the competition, what allows you to achieve the goals you set before you started.

While the miles pass incrementally, fatigue sets in exponentially. Mile 13.1 is not, I repeat not, the 'real' halfway point of the race. Almost everyone feels great at this point. Mile 18 is where things start to get serious, and every mile after that point is twice as hard as the one before: Mile 19 is twice as hard as Mile 18. Mile 20 is twice as hard as Mile 19, but also four times harder than Mile 18. You get the idea!

Since we don't enter this space in our training, it pays to have a clear 'One Thing' or reason to keep you moving when your body starts to push back. Maybe you want to finish before a certain time or pace group. Maybe you are planning on a great post race party. Maybe you are running in the memory of a loved one or to support a charitable organization. Whatever the reason is that you have, know that reason and have it ready to go at a moment's notice!