I think the key is to have a Safety Net. If you're lucky, you get one for free at birth. If not, you need to build it yourself during the first several years of 9-5ing.
Once you know for a fact that you can coast along for an entire year if things go south, life gets a lot better. You can start consulting and not have to sweat the occasional dry spell. You can build income generating products after work or during those blessed dry spells. You can do all that stuff remotely while dialing up your leisure time activity of choice to whatever level feels the most comfortable.
Better still, with a bit o' Safety Net, you'll be able to demonstrate to yourself that you can quickly pick up contract and full-time gigs when you need them. And you can emit artifacts that demonstrate to prospective employers that they should grab on with both hands if you happen to signal availability at any point. That helps a lot towards being able to bootstrap a product business on the side.
Eventually, after much trial and error you'll find something that sticks. I think for me it was something like Job Quittin' Side Project #6 that finally started bringing in enough profit to replace the day job.
Finally, make sure you're having fun along the way. It's not supposed to be a grueling heads down slog for however long it takes before you finally "win". It's life. And it's most enjoyable if you actually take the time to enjoy it while it's happening.
All the best! Let us know how it turns out.