I work out much more for the mental results than the physical ones. I understand that being in good shape is good for my health and life expectancy, but if that was the only motivation I had to get myself to work out... I wouldn't.
I work out for the sense of accomplishment-- that even if I did nothing else productive, at least the day wasn't a complete waste. I work out for the mood-lifting rush of adrenaline and endorphins, the calming, satisfying ache of well-used muscle