as transient as a fleeting cloud (/drifting clouds); ephemeral ? 論起榮華富貴，原不過是“～”；……(《紅樓夢》1513) Of course wealth and honour are transient as drifting clouds.
過眼云煙
as transient as a fleeting cloud;like a puff of smoke;ephemeral 一切榮華富貴都是～。All fame and wealth are just a flash in the pan.
過眼云煙煙云過眼ɡuò yǎn yún yān
在眼前飄過的云煙，一去不復返。比喻很快就消失的東西。as transient as a fleeting cloud, ephemeral, pass from one’s view