白衣苍狗 — “Describes how things or situations change rapidly”

Du Fu was a benevolent person, though he often struggled with his own basic needs, he used his poetry to help others.

Li Guinian was a renowned artist during the Kaiyuan era, highly favored by Emperor Xuanzong of Tang. Princes and nobles often invited him to perform, and he received immense rewards. However, after the An Lushan Rebellion, Li Guinian fell on hard times and drifted to Jiangnan. During a banquet, Du Fu heard Li Guinian's singing once more and penned a poem praising his exceptional talent, expressing: 'Often seen in Prince Qi's mansion, heard many times in Cui Jiu's hall. It is precisely the beautiful scenery of Jiangnan, and in the season of falling blossoms, I meet you again.'

Wang Jiyou was another Tang dynasty poet who lived in poverty, earning a living by selling straw sandals. Yet, he found contentment in his humble life, dedicating his spare time to reading and writing poetry. His wife, unable to bear the hardship, left him, and he became the subject of gossip. To console Wang Jiyou, Du Fu composed a poem that included the lines: 'The floating clouds in the sky are like white clothes, yet in an instant, they transform into gray dogs. Matters throughout history have always been so transient and unpredictable; what in life can one not encounter?' It is from this imagery of changing clouds in Du Fu's poem to Wang Jiyou that the idiom '白衣苍狗' originated, metaphorically describing the rapid and unpredictable changes of worldly affairs.