Your time. Can't get it back. How many days have you thrown away the hours? Sometimes there appears to be a good reason, but usually there isn't. I'm as guilty as anyone of not maximizing my time on earth. Changing ones habits? That's another story.
The highly productive musicians who's lives were cut short, Mozart, Hendrix, Coltrane, Dolphy etc. seemed to be keenly aware that their time was short and yet made the most of it. They didn't just blow off months and months in a pub.