The hardest part of being a teacher

"What do you find is the hardest part of being a teacher?"
"Well, the hardest part for most of the people -- of course, it's not for me, it's not difficult for me, I have gotten used to it -- but the hardest part is that a teacher has to forget everything in his life, in his or her life, OK, before going to a class."
"Why do you say -- what do you mean by that?"
"You see, if you are sad, if you have a lot of ups and downs in your life, when you enter a class, you have to be a teacher full of energy, very happy. You have to forget about all your problems. If you just take your problems to the class, you won't be a good teacher."