I quit my job. I did that because I thought it would be valuable to focus just on the startup rather than have my focus split. It's possible that decision may not have been the best one. I had a job with lots of personal development opportunities and they were willing to let me work part-time on my startup, part-time on that job. In hindsight, that would've been ideal. It might have just been my circumstances, but I think that the two complement each other extremely well. I would have been better at my job as a result of the startup, and vice-versa.

Just do whatever seems to fit your circumstances best. Forget about the startup groupthink on what's better or worse.

Keep your job and start selling the product. Don't take investment capital unless you absolutely have to, and don't quit your job until your profits are high enough that you can do so comfortably. If you do it this way, you'll relieve some financial uncertainty as well as put yourself in a better position to negotiate should you raise money in the future (you end up saying "We have a profitable business" instead of "We have this thing we haven't sold to anyone yet").

Stick to your job. Expect the first idea to fall through, but fourth or fifth one to take off.