The choice to keep wanting to improve may be not nesly whatever one chooses, but it's a choice that is available to all people. Most of us respond really strongly to incentives that come from without, from extrinsic motivation. There are others who have a different kind of fuel that is driven not entirely intrinsically, but very, very strongly intrinsically. I think you're right when you ask the on what sort of gratifications tend to diminish with more of it - money.