1. The depth of my own ignorance.To sound blatantly cliche-ish, the more I read, the more I realize how much I haven't read. The more I know, the more I realize how much I don't know, and how much I will never know. I can echo Will Durant when he says, "Education is a progressive discovery of our own ignorance." And I can see why the preacher warned, "the writing of many books is endless, and escessive devotion to books is wearying to the body" (Ecc 12:12).
Real education seems to have a built-in humility. In other words, if you think you know it all, you've still got a lot to learn.
2. If I want to sleep well and not have nightmares about the Cracker-Barrel, I shouldn't down an energy drink at 10:00pm.