You need to believe in what you do when you start a company.
I also suggest based on the fact that I do work for such a company, which has been successful. Next year is its 20th anniversary. It's an amazing place to work at. You can create amazing work environments out of open source. And while it's quite rare, it's also far from being the only one.
Another commenter says that I seem to ignore the consequences of a failure. I don't. However, I'm surrounded by open source companies and they all seem to be great places to work at. Join us!
When you believe in open source, being able to work in agreement with these values is amazing. I can't imagine how stronger that must be for the one would indeed founded a whole business like this.
It's time people stopped spreading this belief that open source and sustainable business cannot go together.