Yup. Passion can substitute for paycheck to some extent ("I don't earn as much as I would at $mundane-job-X, but at least I'm doing what I love!"), at least for the first couple years - and by then, it's much harder to change your career path.
Exactly. After the passion wears off and you're left with a young family that needs food and clothing and medical care and you can't afford to buy a decent house, doing what you love isn't enough.
