Teacher's story:
Once a friend of mine had a problem with is program but it would only happen from time to time, so he didn't get bothered with it.
So, because I'm an evil person, I did a print in his program with the error message.
After a day debugging, he found the error. He really wanted to kill me.

I'm at college and I was learning Java. While we were practicing in class, one of my friends was having a problem with his code, it was printing that he needed to use java.lang.String.
Because he only told us after class, we didn't have the teacher to help us, so we tried debug it. After a long time, we realized that he was trying to create the class String...
We still talk about it.