That reminds me of a fellow I knew who was trying to teach a new employee how to develop photo negatives in the darkroom of a print shop. She kept carelessly getting stop bath in the developer which tends to make things turn out rather badly. She didn’t understand when he told her that a little developer in the stop bath didn’t hurt but a little stop bath in the developer ruined it. Finally he said he told her, “Look at it like this, the developer is ice cream and the stop bath is cow manure, I am sure that you can understand that a cup of ice cream in a barrel of cow manure doesn’t hurt it but a cup of cow manure in a barrel of ice cream ruins the whole barrel, okay? From then on he said there was never a problem.
I like that.