tā / cháng / shuō / gé / háng / rú / gé / shān / wài / háng / hěn / nán / dǒng / nèi / háng / de / shì

他常说隔行如隔山，外行很难懂内行的事。

He often says that different trades are worlds apart, and outsiders can hardly understand the insiders' work.