Watch the negative words and thoughts. Think instead about all the successes you have had. How about all those hills you conquered? All those long workouts you endured? You are a great person. Relish those thoughts.
Negotiate with yourself
Give yourself permission to simply go to the next water stop, or to the next milestone, or even just the end of the day. Keep repeating that strategy until you see the finish line. Just one more mile before you say one more mile!
If it was easy, everyone could do it. You are the one who will make it. And don't forget the finish line pose!