Have two primary objectives with your startups- to get them stable, solve the big/fun problems etc., and secondly to replace yourself. I know we're all irreplaceable, but the truth is a good businessman can find someone almost immediately to train and groom to take over whatever it is you're doing- releasing you to move onto the next thing. You'll have finished most of the creative stuff that needed you. Then you go back every 6 to 18 months when they have an exciting new problem and save their butts.