I think there's a very big difference between enthusiasm and passion. Enthusiasm is ephemeral. Like with dating, it's easy to be enthusiastically in lust with the romantic idea of start-ups early on. Enthusiasm can fade after a first anniversary. Passion is in the blood. Passion is what keeps you married to your vision even after it gets a little older, has put on a little weight, and delivered you a nest egg or two.

I haven't met any successful serial entrepreneurs who aren't passionate about what they do (whether specifically technology or entrepreneurship in general). Just as well there are passionate entrepreneurs who fail (most of the successful ones did originally).

Enthusiasm dries up. Passion doesn't.