There's nothing like standing in front of 30+ undergrads to make you realize what you really know and what you really don't.
I've never taught statistics before. I do not claim to be a statistician by any stretch of the imagination, but I think I have a working understanding. However, it became crystal-clear to me that I do not understand it well enough to teach it with confidence.
My students had to collect some data to test a weird hypothesis and do a Chi-square test of homogeneity. I gave my first lab the wrong instructions on what they had to sum, and in my second lab I got all flustered trying to explain how the Chi-square value and probability are related, and what that has to do with the hypothesis and null hypothesis... I totally confused myself standing up there so I'm sure they were even more clueless. I just couldn't form the words to explain what was going on in my head!
The lab instructor stepped in to save the day (and my students' comprehension) for the second Chi-square test, and I got to watch him explain it elegantly and succinctly. Definitely something to aspire to.
You never really learn something until you've had to teach it, right?