Ask HN: How do you know if an idea is worth running with?

I'm currently developing a SaaS product in my spare time. It's a tool that I want/I will use that doesn't seem to exist in the market already in any decent fashion. In my own bubble it seems like a great, potentially profitable idea, but I have no idea if that means it's worth trying to make into a real thing? Also, I don't even know how I'd make it a full blown SaaS product by myself.

If the right answer is to just read Hackers and Painters, I'll totally do that. I just can't tell if I'm clouded by my own bias.