I've been self employed in various ventures my whole life, so quitting was more a matter of throwing in the towel when a business became more painful and less profitable than it was worth.
I ran a printing business for a number of years, and started to really hate it, the squeeze on profit margins, heavy competition for a limited market, working with solvents and inks, accounts receivables growing and becoming a full time job trying to collect.... etc etc etc
I finally had enough and just shut it down one day, lived like a pauper for months and went on to the next phase of my life... best decision I've ever made
(funny, in the middle of that crisis I also broke up with a long long term girlfriend as well, so it was all a big time of change and upheaval, but looking back I am glad for it, stronger for it, and better off for it)