I just finished the book Why We Run: A Natural History by Bernd Heinrich. I loved this book. It was the perfect blend of science, medicine, history, running, and storytelling. Mr Heinrich uses his experience training for the 1981 100K Chicago race to discuss the human desire to run.
Describing a moment in his 100K race, he describes feelings all runners can relate to:
...My body is screaming at me to stop, and it would always win if it did not have a mind to play tricks with it, boss it around, and delude it.
To psych oneself up takes self-delusion. That's where the use of logic comes in. Logic is less an instrument for finding truth than a tool that we use to help us justify what our lower emotional centers direct or demand. Lacking this self-delusionary logic, we would be less able to rationalize, and so be unable to succumb to such mad, senseless, crazy things as trying to see how fast one can run 62.2 miles wtihout stopping. Ultimately, our logic may get wacky enough that we see through our rationalizations, and then they don't make sense anymore. This almost invariably occurs sometime around halfway through the race, and you ask yourself, Why am I doing this? Why am I here? Why? There is no answer.
At that point, one needs faith - a combination of ignorance, deliberate blindness, hope, and optimism. It defies logic yet makes us able to strive and to survive. p250