It means: People often ignore and do not understand the great development prospects of a small pine tree that will grow into a towering tree. They wait until the pine tree really towers into the sky before praising its tallness.
This poem comes from "Little Pine" written by Du Xunhe in the Tang Dynasty.
Original text:
"Little Pine"
Since I was a child, I have been thorny in the grass, but now I am gradually aware of the basil. ?
At that time, people didn’t know the Lingyun tree, and they waited until Lingyun began to flourish.
Author: Du Xunhe (846-904), a native of the Tang Dynasty, named Yanzhi, Jiuhuashan native, Han nationality, from Shidai (now Shitai, Anhui), Chizhou, Tang Dynasty. Born into a humble family. He went to Chang'an several times to take the exam, but he returned home after failing to pass. When Huang Chao's uprising army swept across Shandong and Henan, he returned home from Chang'an. From then on, he "lived in the tobacco industry for fifteen years" ("Coming out of the mountains after the chaos and met with high-ranking officials"), and lived a life of "the world is poor and the people are poor, and the mountains are fertile for farming" ("The Works in the Mountains after the Rebellion"). Later, he traveled to Daliang (now Kaifeng, Henan Province) and presented 10 poems of "Shi Shi Xing" to Zhu Wen, hoping that he would save himself from corvee and pay too little for his work, which was not to Wen's liking. When he stayed in the monk's temple, Zhu Wen's subordinate Jingxiang persuaded him to "cut off the ancient style a little, and then he can enter the body", so he wrote thirty chapters of poems in praise of virtue to please Wen.