It is almost a household word that a threesome must have a teacher, from the Analects of Confucius. The original text is: "Confucius said:" In a threesome, there must be a teacher; Choose the good and follow it, change the bad. Confucius said, "There must be something to learn from what others say and do. Choose others to study hard, see other people's shortcomings, reflect on whether you have the same shortcomings, and if so, correct them. "