Lu You (Southern Song Dynasty)
The ancients learned nothing, and it takes time to grow old.
What you get on paper is so shallow that you never know what you have to do.
It means: the ancients spared no effort in learning, and they often didn't achieve anything until they were old. After all, the knowledge gained from books is not perfect. If you want to understand the truth deeply, you must practice it yourself.
The word "unique knowledge" means profound understanding.