Hello, I am very happy to answer your question. The answer is as follows:

If a young man does not work hard, he will be sad.

As the saying goes, if you don’t work hard when you are young and strong, there will be no use in being sad when you are old.

Source: "Collection of Yuefu Poems·Chang Ge Xing": "When hundreds of rivers reach the sea from the east to the sea, when will they return to the west? The young will not work hard, and the old will be sad." Yuefu of the Han Dynasty, Han Dynasty.

I hope my answer is helpful to you.