I actually have a different take on this. I was building a side project 2 times in my past, to a point where there was some buzz around these side projects. And, I didn't have a job when I was working on these. However, as the products were nearing completion for V1. I got very good offers for contract work. I also had debts, so I took up the jobs. However, this led to the products failing to get any traction.

So, if you are planning to leave a job and have a good product which is getting you even half of the money you need. Leaving your job will only increase the chances of success. However, hanging on to the job while working on a product is going to be much harder.