Tell me your job quitting stories

For motivation, I want to hear examples of people who quit their jobs to work on an idea for a product or service.

Bonus points if it was a good job that you liked and leaving was tough but worth it. Extra bonus points if your product is/was successful :)

Hit me with it! The good and the bad, I want to hear them all. How far along was your product when you quit? When did you make the decision? What happened afterward?