How does the ending of this poem express the author's feelings? Try to analyze what is the root of Du Fu's sadness.

Looking at the Moon is a famous poem by Du Fu, a famous poet in the Tang Dynasty. By describing the majestic atmosphere of Mount Tai, this poem enthusiastically praises the lofty momentum and magical and beautiful scenery of Mount Tai, reveals the love for the mountains and rivers of the motherland, and expresses the poet's ambition and spirit of not being afraid of difficulties, daring to climb to the top and overlooking everything, as well as his great ambition of being independent and helping the people.