People often ask what inspires me to do an Ironman. To me everyone is capable of competing in an Ironman, it is not as difficult as it appears. An ounce of discipline, a pinch of fortune, a teaspoon of insanity, and a whole lot of time all combined makes for an Ironman finish.
What motivates you to get off the couch is different for everyone. For me it is not one thing, it is a culmination of things that I can't fully articulate. It's because I can, I am able bodied and healthy and I love being outdoors. It's because I know people my age and younger who can't because they struggle with and manage debilitating diseases. If you look, motivation and inspiration are everywhere.
As an example, yesterday on my 70 mile ride I saw a guy who had his left leg amputated half way up his thigh. There he was peddling along on one leg--no prosthesis just using his one good leg and he had the broadest smile. Do you have any idea how difficult that is? Get on a trainer and try an hour of one-legged drills....or five minutes worth. It takes serious strength and fortitude. See, motivation and inspiration are everywhere you just have to open up your eyes to it.