The idea had been taking some shape prior to reading this fellow's account, but had never taken much shape - after reading his account, however, I was gripped by the notion. I would not be able to shake it until I had a 100 mile run successfully under my belt.
Others may be motivated by different accounts, but this is the one that did it for me: How to Run 100 Miles.
It's a long page, so besides linking to it, I've also pulled out the specific passage that struck a chord. Here it is, broken into several sections to make it easier to read:
"When the sun goes down it can take your spirit with it. The darkness will suck the life right out of you if you allow it to. Your mind must take full control at this point because your body wants to sleep. Allowing your mind to overcome the body is what will help you persevere throughout the nighttime hours. It' s a matter of how much you want it at this point.
"Think about what it is that motivated you to attempt to run the distance in the first place. Were you teased as a child? Were you picked on by a friend or family member or do you just feel the need to prove something to yourself? Whatever it is use the energy from these situations that may normally cause anger or frustration to your advantage.
This last statement in particular gripped me - I needed to know what that feeling was like, and would not rest until I found that out!
"Keep your mind occupied with something other than pain or distance remaining. If with someone talk as much as possible. Silence normally means you're not staying focused and you're allowing thoughts of doom and gloom to enter your mind. If you persevere until the sun rises I promise you new life will be given."