Discussion - Why do you do it?

I wasn't sure whether to post this here since what I'd like to discuss is not directly linked to startups, the web, funding, and so on. But, I figured it would gratify one's intellectual curiosity as the guidelines say :), and also shed some light on how entrepreneurs and like-minded people view the world.

So what I'd like to ask you is seemingly simple: is there a higher purpose to what you do? Do you get to work because you believe your actions will benefit mankind, because you enjoy it and think that is all that matters? Or do you do it because it brings financial gains which help you achieve your other dreams? Or is it something else? I'm not trying to point out a good or bad way, I'm just really curious as to what drives people to go through sometimes unbearable difficulties, in order to achieve something.

Thank you.