一缕青烟尽恰似旧人归
[yī lǚ qīng yān jĭn qià sì jiù rén guī]
When a wisp of smoke fades as if old friends return. This depicts nostalgia or a poignant moment where fleeting sights remind one of the past, like seeing smoke vanish and reminiscing about old acquaintances or past days returning momentarily only to depart just as swiftly.