Sleep. It's one of those things you take for granted until you aren't getting enough. I remember, through a thick fog, those sweet days of having infants, when I never got enough sleep and existed in a sleep-deprived haze. None of my kids slept through the night until they were at least three years old. By the time my fourth child was old enough to sleep through the night (or, more accurately, get his own glass of water), I had been sleep-deprived for 10 years. At first, I hardly knew how to sleep all night. Then I couldn't get enough sleep. Finally I settled into what I thought was the rest of my life with a reasonable amount of sleep.
Ha. That was before I had teenagers. A friend of mine once noted that a lot of parenting occurs after 10 pm when you have older teens, and she was right. Teens have a shifted circadian rhythm that makes it hard for them to go to sleep early and get up early, so they are at their best in the (late) evening, just when I am ready for bed. As much as the idea of going to bed at 9:00 appeals some nights, I don't unless I am exhausted, because 10:00 is when the boys come out and are willing to talk to me. So I stay up reading (ok, this isn't all maternally motivated - after 9:30 is the only quiet reading time I ever get) and give them a chance to creep out of their caves. Some nights, my talkative daughter hits me with an emotional crisis that really could have waited until tomorrow (from my perspective, not hers) and I sort of wish I had gone to bed. But other nights, one of the boys will actually start telling me things about his day or his friends, or bring up a question he has, and it is worth it. I may not be scintillating at the hour, but at least I am present. So I guess it is worth doing without enough sleep. Yawn.
For a fun game to see how sleep-deprived you are, try the Sheep Dash. I rated Ambling Armadillo my first try and a cup of coffee was suggested. Oops. On the other hand, I rated "getting enough sleep" on the Epworth sleepiness test, so maybe the Sheep Dash was testing my computer-game reaction speed (which is very unpractised) more than my alertness.