As the teacher of a Sunday school full of 10 year olds (they will ask you anything), I was asked, "Coach do you have mean or ugly thoughts?" I admitted I had both and was quickly thinking what to say when another 10 year old saved me. He said, "my parents said bad thoughts are like birds flying through a forest, you going to have them just don't give them time to make a nest." wise parents!
I have not heard the subject explained better.