What is the intention of Du Fu and Guigui in ancient poetry?

In late spring and early summer, when visiting scenic spots, you can often hear "cuckoo! Bugu! " The cry, or "plant corn early!" Plant corn early! "Or crying," go home! Why don't you go home! ".This kind of voice is crisp and sweet, very sweet; When I heard "it is better to go home", I felt sad and sad. The villagers call it "cuckoo", but it is actually cuckoo. It is a spring bird and a lucky bird, because it is also called "cuckoo bird" and "Zigui bird". According to legend, it was incarnated after the death of Emperor Du Yu, and Du Yu was an enlightened emperor in history. He saw that the tortoise had made great contributions to water control and the people lived and worked in peace and contentment, so he offered to give him the throne, and soon he died. After his death, he became a cuckoo, and he crowed day and night.

Sub-rule:

Zigui, also known as cuckoo, is another name for cuckoo. According to ancient legends, its predecessor was the king of Shu, named Du Yu and Wang Di. Later, he died of mourning for his country, and his soul became a cuckoo, crying very sadly.

(The above is taken from Baidu Encyclopedia)

So cuckoo and Zigui refer to the same animal. Because there is a sad legend behind this animal, they often become sad, sad, bitter and sad images.

There is a saying in "I heard that Wang Changling moved to Longbiao Kiln Left with this letter": Huayang fell to the ground and wept. Li Bai used the image of a devil to express his sadness at someone being relegated. Although there is a political mapping, it is mostly a sad artistic conception.

There are also the cuckoo's bleeding and crying and the ape's sobs in Bai Juyi's Pipa. This is also to express that the place where the author was relegated is desolate and miserable, and people's mood is lonely, lonely and sad by Du Fu's sad artistic conception.

In Li Bai's Difficult Road to Shu, there is also a moonlit night when the cuckoo's melancholy voice comes. Sentence, artistic conception is also sad and sad.

There are many ancient poems by Zi Gui and Du Fu. Generally speaking, they all show a feeling of sadness, bitterness and sadness. But it needs to be explained in a specific environment.