One couplet is skillful and fluent, fluent and implicit. It shows the poet's ingenious thinking and deep affection in using function words to form neat antithesis and vivid harmony, which is also the reason why this word is famous. But what is worth pondering is the meaning of this couplet. The fading of flowers, the disappearance of spring and the passage of time are irresistible natural laws. Although it is useless to regret lingering, they all say "helpless", which is inherited as "the sun sets"; However, in this late spring weather, I feel not only helpless disappearance, but also gratifying reappearance. Isn't that swallow who came back to dance like an old acquaintance who built a nest here last year? This sentence should be "when will you come back". Falling flowers and the return of Yan are also eye sights, but once they are associated with "helplessness" and "deja vu", their connotations become very extensive and their artistic conception is very profound, which is a symbol of good things. The interweaving of regret and comfort contains a certain philosophy of life: all the good things that are bound to disappear can't stop them from disappearing, but at the same time, there are still good reappearances, and life will not become nothingness because of disappearance. It's just that this reappearance doesn't mean the reappearance of beautiful things intact, but "deja vu". The reason why this word is a household name and widely read is that it is thoughtful in love. These words seem to inadvertently describe common phenomena, but they have philosophical significance and inspire people to think about the universe and life from a higher level. Ci involves such a profound thought that time is eternal and life is limited, but it is very implicit.