Isaac's Fairy Note #30:
If a fairy does something you don't want, do NOT say "Thank you" because they would just do it more. Fairies are very generous but they work under their own logic and most scholars have given up on trying to reverse-engineer it. A professor of fae, Elbum Elbumek, once discovered that fairies have up to eighteen possible answers to a "yes/no" question. I actually met him once at a wizard convention. He had been transmogrified into a desk and was very bitter about it, but he was a nice guy, otherwise.
(The note went on to describe how they had a conversation about desk lamps.)