Motivation

What makes a person go out of there house and workout at 9 o clock at night? Or go that extra mile when you have already gone seven? Or come home after working out and do another twenty minute workout? What is that. And then better yet why doesnt whatever it is that makes me do all these things stop me from doing what I shouldnt do? Why doesnt it stop me from drinking a regular coke now and then or eating a heaven scent donut? Where is that thing. In my mind I think of all the working out I will have to do for the said item yet I eat it anyway. Motivation is funny like that.