there are a few paths you can take to arrive at this conclusion, and i've done all of them:
the first time i quit my job to go full-time as a founder was early 2014. i didn't have any freelance gigs lined up, and only a few thousand dollars in savings. i did it anyway. ultimately i became a much better freelancer (marketer) than founder, and i shut down the business after ~1.5 years of hustling and spending all my earnings.
the second time i did it was my most successful venture (Fomo), except i didn't quit until we were already making $30,000+ per month in recurring revenue. even then, i didn't get my first paycheck for another ~year. we reinvested everything back into the product.
books like Profit First helped me think more intelligently about reinvestments vs dividends as a business owner.