Was reading Meb for Mortals recently and Advanced Marathoning a while back when noticed both authors, despite being elite long distance runners, mentioned the mental pressure at kilometer 30+ at marathon races. That is very true. No matter how fit you are, you start feeling breaking apart at that mileage and that is where the mental challenge starts. You try to put yourself together while your body wants to be out. As soon as you get close to 40km mark, the euphoria of seeing the finish line soon would be enough to keep you going to the end.
Succeeding at such a challenge takes believing in yourself. If you doubt about your abilities, you have low mental power at that stage of the race to overcome the down-feeling. Worth mentioning there is a fine line here between realising the risk of getting injured, and having confidence to push through the pain in hope of success. That is your call, but if you have trained enough, I would say believe in yourself and push!
Well, believing in yourself is always easy on paper, sometimes real tough in real life. Sometimes you can be talked through, sometimes you have to practically prove it to yourself.
A while ago I was challenged to jump over a bench, and although I was able to jump that high, I just could not do it. My mind kept telling me my feet would hit the edge of the backrest. There were two benches, same height and next to each other. I practiced a lot jumping over the benches with no luck jumping over from stationery position. The best I had done was with a little step forward before jumping. Today I thought of a trick to break my mental barrier. I used a sticky tape to link the top edges of the benches and then tried jumping over the tape. If I hit the tape there would not be any danger, so I just jumped, and it worked. Once I practiced a couple of times I jumped over the bench with no hesitation, and bang, nailed it. Looked like a small step, could be a giant leap for one.