“I’m good at blowing bubbles with bubble gum. I have yet to charge anyone for doing it.”
I think it’s implied that this only applies when there is a demand for the service. Were you to find that there’s a large audience for your displays, I bet you’d at least pass the hat around before doing another one.
This is a good take, but I think I like the Feynman better (which I have to assume has appeared months and months ago):
“The first principle is that you must not fool yourself, and you are the easiest person to fool.”
From a different angle, there’s also the Heinlein: “Your enemy is never a villain in his own eyes. Keep this in mind; it may offer a way to make him your friend. If not, you can kill him without hate — and quickly.”