flog a dead horse
成語所屬單字horse
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
徒勞無功
To waste effort trying to do something that is no longer possible.
例句
Arguing about that old rule is flogging a dead horse.
Brian realized he was flogging a dead horse and gave up.