I didn't invent the metaphor -- it's a hollywood thing -- but I like it.

Hunger implies starvation: you must do something in order to survive.

And it also covers what happens when you finally eat (grow a business) -- you stop being so hungry.

I think the really, really successful entrepreneurs are those who are as hungry with a billion dollars as they were with a buck-and-a-half. i.e., they never lose that hunger.