We were subjected to school assemblies in which motivational speakers, usually fat, badly-dressed men, would badger us for an hour or two. One such speaker, this time a fat, badly-dressed woman, held up a piece of paper, and informed us that this was our self-esteem. She then proceeded to go through all the rotten things that were said to us (or, we suspected, her) in the course of the day.
"You're ugly."

"No, you can't sit with us."

"Jesus, you honk like a good'un, Cheryl."
With each insult, she would tear off a strip of paper. At the end of the day, evidently, one is left with a very small scrap of paper, or self-esteem.
It was common in the following week for children who had been insulted to pick up a piece of paper and rip it with a mock-sad face; that fat useless jabba had accidentally given children a decent defence to any insult.