I've recently quit my job to work on my startup full time. I do have some money saved up and am living cheaply. At some point you have to take a chance on yourself and do what you want. Life is too short to be working on things you don't want to do; that was the primary reason for me to devote myself full time. I also wrote about this in slightly longer prose, if you are interested:

http://www.akashkgarg.com/essay/therighttime.html