https://zh.apacode.com/post/learn-and-practice-it-its-not-like-talking-about-having-friends-from-far-away-its-fun-people-dont-know-but-dont-feel-shy-its-not-like-a-gentleman
學而時習之,不亦說乎 有朋自遠方來,不亦 樂 乎 人不知而不慍,不亦君子乎