For whatever reason, I try to follow through on things that I start. That's not to say quitting is bad, on the contrary, quitting all the superfluous stuff enables one to follow through on the larger things. Yet sometimes doing what you said you would do is so simple. Just this week I told some of the mechanics I would bring them food if we passed the test, a few days later we passed the test and I brought in bagels. It was a little awkward as I stood there telling them the reason I brought bagels, so I left before they had a chance to start eating. As I walked out of the shop I had the feeling that I followed through on something, no matter how small it may seem to me, I did it. Maybe this would seem insignificant compared to things like Mt. Everest and running records and such, but it's all part of the story, and it's the human connections that are often the most difficult.
Moral of the story, follow through, when you can.