The thought, "is this a good long-term career choice?" isn't in the equation. That's for people looking to build a career. This is your one great idea that will make you rich, fuck a career. You are your boss from now on.
If your thought process doesn't look like that than maybe you just haven't stumbled upon that great idea. The idea that strips every rational bone out of your body, that keeps you up at night. Or may you just don't have the risk tolerance for entrepreneurship.
It's a fairly cavalier mindset, but you have to have that kind of naivete to outlive the struggles of starting a business.