Right now I am tired and I don't want to ride home. I could just hop on the subway take it to the end of the line and then I would only have about 1.5 miles left to ride home. But I won't. Partly this is because I need the exercise. Mostly its because I am committed to doing the biking. It makes me feel good and I know that I will be happier if I don't shirk. So I don't. Its much easier to make a decision once then to make it many times.