Listening to my lectures on Medieval Church on iTunes, Justin Taylor heard me make this statement which is now, ten years on, somewhat amusing:

"I'm recommending GR Evans on Bernard of C based on her reputation, even though I haven't read it yet. I'm playing the percentage game, as it were."

It reminded me of the two golden rules of teaching: if you have not read a book, always make it clear to the students you have not done so; and (tangentially related) if you do not know the answer to a question, admit you do not know the answer.  The desire of the teacher to appear omniscient must be resisted at all costs.  Education is about teaching, not creating an image of genius where none really exists.

Oh, and if a friend tries to blackmail you with a quotation from your dark past: take the initiative and go public!