Just the thought of running a marathon can cause me to break out in a sweat. Clearly, not the event for me. But more and more people are taking on the incredible challenge of running - or perhaps crawling - over 26 miles to the finish line. At yesterday's Boston Marathon, a former Marine did just that - crawled the last four miles of the marathon because his legs finally gave out on him. He was determined to finish, not just for himself, but for the fellow Marines he lost in Afghanistan. Watch this guy's gritty and gutsy finish. It will make you proud.