1.)I have expenses that need to be paid. My current savings could get me through maybe 5 months? and then what? 2.) I like knowing I have a backup plan. I think its what, 5% of business launched that succeed? Despite working my way through the other 95% of fails already, having an incredibly solid business plan, and (for the first-time)a passion for the product; its still nice to know I can provide for myself and my family. 3.) This is the big one... I need money for my business!. II can hire faster, advertise easier. How's a little guy to compete with the big boys without a hefty budget applied to smart marketing!
With all that said, I have considered dropping my hours, or my job entirely, but why take the risk? there's nobody in my space. There's no rush! Why take a risk of losing everything, when there's no risk of losing your idea to someone else.