flog a dead horse
成語所屬單字dead
flog a dead horse — 慣用語
1. To waste effort trying to do something that is no longer possible.
1.慣用語
釋義
白費力氣
To waste effort trying to do something that is no longer possible.
例句
Arguing with him about politics is flogging a dead horse.
Trying to sell ice in winter is like flogging a dead horse.