Why don’t you play mahjong with your mother-in-law?

The reason why you should not play mahjong with your mother-in-law is: you will inevitably win when you play mahjong with your mother-in-law. But after you win, your mother-in-law will of course be very unhappy and secretly give her your daughter (your wife) You will have to endure "class" and the like, so the mother-in-law cannot win!

This sentence comes from the classic line of "Chinese Partner": Never play mahjong with your mother-in-law - you can't win. Never sleep with a woman who has more ideas than you - you will be plotted against Sadly, never start a company with a friend - it will hurt the friendship due to profit.