Only when the sky can fall and the earth can be cracked can we dare to leave the king. It comes from that book.

This sentence comes from the folk song "Thank you" of Han Yuefu.

The original text is like this: evil! I want to know you,

Long life and never die! A mountain without a grave,

The river dried up,

Thunder bursts in winter,

Rain and snow in summer,

Heaven and earth,

I dare say goodbye to you.

This is an oath to express love and loyalty. The author describes an impossible separation with five impossible natural phenomena. Strong and frank feelings, simple and pungent style. "The mountain has no edges, and the heaven and the earth are in harmony, so I feel absolutely separated from you" means that when the mountain has no peaks and the heaven and the earth are in harmony, I can leave you.