history
Closing couplet of Li Shangyin's (李商隐, Late Tang) 《锦瑟》: 此情可待成追忆，只是当时已惘然. (Could this feeling have waited to become a memory? At the time it was already lost in haze.) The poem, famous for its obscure imagery of a zither, butterflies, and pearls weeping under moonlight, is widely read as a lament for vanished love or lost ideals.
usage
可待 is a rhetorical 'could it have waited?', meaning 'no, the feeling was already passing into memory even as it was happening.' Deeply melancholic; don't use for trivial nostalgia.
