I was asleep by 8:30 last night, worn down by an ear infection. I planned on doing some work in the evening but my body said, "No, you're not," so I crawled off to bed.
It was a reminder of the beautiful and regenerative virtue of sleep to one who thought no reminder was necessary. As a rule, I try to get to sleep by 10:30 at the latest and even follow a regimen to produce some solid rest; e.g., no caffeine after seven. Things build up unnoticed, however, and the physical side eventually tugs at the mental and declares time for a break.
I've written here before about the unrecognized role that fatigue plays in organizations. Performance starts to decline because people are simply worn out. The boasting about long hours spent at work has never impressed me. Far more admirable is the person who does as much in three hours as others do in twelve.
Instead of long hours, it is wise for our days to combine real effectiveness with some serious sleep. Each supports the other.