老大徒伤悲 — “To lament one's wasted youth or unfulfilled potential in old age”

The idiom "Lǎo Dà Tú Shāng Bēi" (老大徒伤悲) originates from the ancient poem "Chang Ge Xing" (长歌行), found in the collection "Yuefu Shiji" (乐府诗集). In this poem, the author uses the metaphor of mallows in a garden to illustrate how one should spend the prime of their life—youth.

The poem describes: "Green, green mallows in the garden, morning dew awaiting the rising sun. The warmth of spring bestows its grace, all living things burst forth in radiance. I often fear the arrival of autumn, when yellow flowers and leaves will fade. A hundred rivers flow eastward to the sea, when will they ever return westward? If one does not strive in youth, one will only grieve in vain in old age."

Through this vivid imagery, the poem emphasizes the preciousness of time, particularly youth, urging people to exert themselves and make good use of their golden years, lest they face unfulfilled dreams and sorrow when they reach old age.