The million dollar question, I'll let you know if I find the answer!

I wouldn't underestimate the luck part though even if you do come up with a brilliant well executed idea.

I've acquaintances who spent years trying to commercialise side projects that have eventually come to nothing. A lot of disappointment but I guess you've got to put the hours in and try something to even have a chance.

Personally always thought the idea of something low key with a continuous income stream sounded the most realistic, as others in this thread allude to. But you still need the idea, the execution and the luck.

There is no quick fix besides working in an industry that's valuable and has lots of broken problems to solve. As I alluded to in a comment I made elsewhere on this thread, it might be valuable to use this to think about your next role. Is your current role in an industry that doesn't expose you to these problems, and would you rather get more exposure?

For me, I got a lot of exposure to these problems in the time I spent working at startups using technology to solve big problems in large industries that aren't conventionally "tech" but this is a long term play; it took me a decade of doing this to start to develop a perspective on where my previous companies, as great of a job as they did, still left certain problems unsolved, problems I would go on to solve at my own company. This isn't a quick solution to your problem but it does work.