Two to four score,
Maybe less, maybe more:
Make it worthwhile.
I've been thinking about what motivates people. We get bored, our parents or loved ones tell us to quit laying on the couch when we're young--I doubt we're conditioned, Skinner-style, into doing the things we do in life. If there isn't some worldly reason why we do them (death and taxes), we're enigmatically attracted to them. Do we even know what we do? For my part, I feel compelled by some force, a sort of spirit which I call an ahtman, when I'm at my most creative. So much of the rest feels like hapless planning and strange fortune.