A TEACHABLE MOMENT
Shamelessly lifted from Patrick Reardon on Mere Comments:

An accomplished teacher here in Chicago, and a regular reader of this page, sends the following account of his first day in school this year:

During my first day of school I was going over a hand out entitled "Great Expectations" -- a summary of what I, my students, and their parents should expect this year. One of my expectations for my students was: "I expect you to make mistakes and learn from them."
A hand shot up. "Teacher, how do we learn from our mistakes?"
I went up to her and said, "Hold out your hand." She did and I slapped it smartly.
"Hold out your hand," I said again.
"No!" she replied.
"Congratulations!" I said. "You have just learned from your mistake." I turned to another student. "Hold out your hand."
"No!" he replied.
"See, you learned from her mistake. The only way we humans learn is by making mistakes. Thomas Edison made 1,000 mistakes before he invented the light bulb. It's better to learn from other people's mistakes. Do you know what we call learning from other people's mistakes?"
"No," the class answered.
"We call it History!" I proclaimed.
Another year of teaching had begun.