I don't think much of the word 'inspiration'. I'm too much of a cynic/realist/skeptic to think that because someone else does something that I can do it. I have plenty of self esteem without using others as examples of what you accomplish by trying harder. You need this just to start on the path towards running a marathon. You need to have the faith that you have the strength and motivation to do the required work. I'm not much for 'faith' either, but for something of that magnitude a helping of intentional blindness is an asset.
Then there's this guy. I watched this in awe of him. It made me want to work harder and strive to do better, because he shows that in the face of long odds, you can accomplish awesome things. That's the definition of inspiration.