From what I've seen it all comes down to powerful drives of personal hopes, dreams, and fears. We have visions of the person we want to be then we try to set ourselves up to be that person or we have inner demons which drive us to something we believe will comfort us or keep us safe. It sounds trite to say it, but knowing what you are capable of, what you are actually willing to do, and your long term interests brings a lot less waste and drama into your life.
Knowing all these things and conciously reviewing them as we make decisions helps a lot but I know with absolute certainty that I still want LOTS of ice cream and I'm certain that the fast metabolism that I don't want to have grown out of will keep me sexy-slim!
I agree that it is the human drive that causes us to behave in the way we do. Maybe it's THE reason why we do anything really. And yes, who doesn't love ice cream right? :D