[kbutler]

Part of the reason is the potential upside: why should you "work as hard as a start-up founder" without the potential payoff of a startup-founder? (Probable value = size of reward * probability)

Another big part is self-determination: work on what you feel excited about. A startup can also add intangibles like experience, excitement, independence.

Will your current job help prepare you to take that "something really hot" to market? Will you be likely to even find that "something" with all your energies devoted to your current job?

I'm currently a captive employee bootstrapping some development on the side, and have previously been an early employee in a small startup, so these are factors I evaluate for myself.