where the market is great and returns 15-20%, you don't blow all of that excess money. You keep your expenses similar to your average years and keep the excess gains from those great years to help out with the down years.

Nothing is foolproof. You be flexible and make adjustments as necessary. Maybe you get a temporary part time job you don't hate for a little bit. You don't need to make a ton of money, just enough to close the gap between your expenses and the less than expected gains for the year.

Also, in the perfect scenario you never even touch your initial principle (in fact it will likely grow even larger) so you have that as a buffer if need be where the principle maybe gets drawn down temporarily during a bad year and then you can build it back up in the better than average years.