What keeps you going?

Really, just a deep rooted desire to constantly improve. It's like an addiction. I can improve some aspect of my life, or get better at a specific skill and then that just turns into a gnawing feeling that I could probably learn even more or do it even better. I guess it's kinda bad too because I'm never satisfied. It's like I get to the top of the mountain just to find out that this was just a huge hill at the base of another much larger mountain.