This sentence comes from the poem "Error" by Zheng Chouyu, a modern Chinese poet. This poem describes a woman waiting for the return of her beloved, and the line "My Dada's horse hooves are beautiful mistakes. I am not a returnee, but a passer-by." The poem describes when the woman hears the sound of horse hooves. She mistakenly thought that her sweetheart was back, but found that someone else was passing by her window on horseback, which embodies the woman's melancholy and loss.
At the same time, this sentence also hints at various illusions and misunderstandings in life. We sometimes mistakenly think that something is what we want, but in fact it is just a passer-by, just passing by. This sense of passing through can also be extended to the impermanence and changes of life. We are constantly pursuing and changing, but the real destination may not be on our way. This philosophy of life is also the profound meaning of this poem.