The trick to long sustained endurance is to give your primal mind no option for escape. You cannot, even for a moment, give that primal mind of yours any inkling or idea that there could be an escape, a way out. The moment you let that idea in your head it will begin to fester, slowly building, slowly growing until your only hope is to quit. The only way to endure through the worst of things, is to give the mind no other option. I have read a few books from prisoners of war. They share their survival stories, and without exception, they all indicate that death comes to those who get an idea in their minds that there is a hope for escape. The idea that there is pending
“way out” of the misery, builds in the prisoners mind where they become so obsessed by it that they no longer do the things that those that endure do to survive. Disease increases, they stop eating, the let small sores and other things get worse. Then when the supposed hopeful moment does not arrive they slip into despair and death.
There is no way out of this alive, there is no escape, there is only endure. Rather than despair, the dogged determination to survive, to persevere despite all the odds is what keeps the human soul alive. Chase away any thought of escape, and think only endure.
Anyone who has ran long distances understands this intimately. Sometimes I will do laps around my neighborhood, passing by my house several times. The reason is that I want to test my resolve. The temptation to quit, to go inside and rest, get a drink, take a nap, eat some food, or whatever the excuse pops in the mind. You have a choice. If you consider one of those excuses for more than just a moment, then you are done. You have quit before you know it. As you make the next lap, your mind will start working on you and before you know it you are walking through the front door only finishing half of your planned run time.
You must, absolutely must, NEVER accept the thought that you can quit. You must continue, you have to continue and there is no way out. That is how you finish 30, 50, 100 mile races. There is no way out, only through. Of course there are times when even the most resolved person will fall to crippling issues, but baring a bone sticking out of my leg, I am going to finish the planned mileage. That is the gritty, determined, no excuses mentally that it takes to endure.