I really worry about that. I have already taken a lot off the table, and am very comfortable even though I live way below my means. The dilemma is when to cash in when the business keeps growing... Its difficult to decide the right time.
I met the founder of a website that sold to Demand Media, that has since blown up into a large property. Of course, Demand probably grew it faster than the founder could have on his own, but nonetheless, the founder was noticeably distressed that he sold too early.
As per Donald Trump - $12 million will get you comfortably set for the rest of your life and provide with lots of spare cash to do stuff that you can't even think of now.
As a counter-point, I have several friends who had nice companies and outstanding offers in the late 90s who could have sold but did not do so because they told themselves that they were going to make the company _huge_ and better offers were always going to come knocking (because for the previous couple years they always did.) When the bubble popped they were left holding nothing and a couple of them are still obsessed with the could'a, should'a, why-didn't-I moment that passed them by.
If you succeed once it will be easier to do again and you will not feel the same pressure to cash out because you will always know that if the current venture blows up you have a comfortable life banked away. Consider the idea that exiting now give you the freedom to exit whenever you want on future ventures by just walking away and trying something else...
