This lesson wasn't directly taught to me by an adult. In fact, it's a lesson I learned multiple times by myself, and I guess you could say I taught them to myself.
The first is that the "good" kid can get away with things based on his or her reputation alone. I first learned this when, for whatever reason was in my 2nd grade mind, I decided to pull a classmates chair out from under her. It wasn't as direct as that, though. We stood up to deliver the pledge, and while we were waiting, I went over, slipped by foot under her chair leg and pulled it just a little bit towards the kid who sat behind her.
Of course, when she went to sit down, she missed and ended up on the floor. I felt terrible for many reasons. One, she actually could have gotten hurt (something that didn't occur to me when I did it). Second, she was really embarrassed. I guess I was thinking it would be funny, but no one laughed. Finally, Tracy Stoneburner got blamed and punished for it. After all, he was a bad kid who did bad things. It HAD to be him. But it wasn't.
I learned that it's not funny to have people fall because their chairs aren't there. More than that, though, I learned the bitter taste that's left when you let someone else take the fall for you. I should have been blamed. I should have been punished. I should have had to do all the things he had to do. But I didn't because the teacher considered me "good". I also learned that, judiciously timed, good kids can do bad things and get away with them. That scepticism has stayed with me always.
In some ways, this lesson has made me a better teacher because I don't automatically believe anyone. I know that everyone has the power to be good, as well as the power to be bad. Most of the times, it's self-control and opportunity that are the true guides.
I also, over time, learned the importance of keeping secrets, because mine weren't kept, as well as the vital importance of not judging others. You never really know what others are going through. Finally, I learned to expect people to talk about me, if they were talking to me about other people. As such, I'm never disappointed when I'm betrayed, made the scape goat, or find that I've been sacrificed for the sake of another.
My lessons, well learned, made me cynical.