論ろん語ご読よみの論ろん語ご知しらず

expression

knowing a theory without being able to apply it

Idiomatic expression referring to someone who has book knowledge but lacks practical understanding or ability to apply it, originally from the Analects of Confucius.

• 彼かれは経けい済ざい学がくを専せん攻こうしたが、論ろん語ご読よみの論ろん語ご知しらずで、実じっ際さいの投とう資しには失しっ敗ぱいした。

  He majored in economics, but he was all theory and no practice, and failed at actual investing.