From Lu You's Reading on a Winter Night in the 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.
translate
The ancients spared no effort in learning, worked hard when they were young, and achieved nothing when they were old.
After all, the knowledge gained from books is not perfect. If you want to know things thoroughly, you must practice it yourself.