The player who teaches a strong move gives away an advantage to improve the company.

Handing over the move that beats people costs you something concrete and buys something less obvious: better opponents, and therefore better games. Whoever does it has decided that the quality of the evening matters more than the score, which is a different aim from the one the game seems to set. It is also how any group of players gets stronger, since knowledge kept private stops with the person keeping it.

If you are the strongest at something in your circle, teach one thing you have been quietly relying on. You will lose a few easy wins and gain opponents worth playing, which is the better trade over a year.