That being said, if it were easy, everyone would do it. Overcoming adversity is what makes the juice you get out of the lemon all the more sweeter. On a macro-scale, reading about Meb Keflezigi's return from injury to win the 2009 New York Marathon is extremely heartlifting: Before winning New York, his last quality marathon was the 2006 Boston Marathon(a span of 3 1/2 years).
On a micro-scale watching Heather Dorniden's 600M incredible victory in the 2008 Big 10 Indoor Championships so neatly encapsulates Winston Churchill's quotation:
"Never, never, never give up."
Running itself, going from stillness to motion, is a minor act of overcoming the tendency or inclination of stopping or resting when tired. It's how far you go in overcoming the urge to give in, how hard you work in spite of all the obstacles that makes the destination and journey that much more enriching. How far do you want to go?