Ask HN: Do what you're passionate about”

It's often said that "you should only do a startup in something you're passionate about", but I sometimes wonder if that applies to many of the successful people and startups.

Can someone really be passionate about CRMs? About payment solutions? About mobile games funded by "whales"? Even something like Uber.

Maybe these apparent contradictions have solutions like: the founders like having a business, making money, etc. Maybe they have motivations that are fairly different from my own.