beat a dead horse

Idioms  

1. Also, flog a dead horse. Try to revive interest in a hopeless issue. For example, Politicians who favor the old single-tax idea are beating a dead horse. From the 1600s on the term dead horse was used figuratively to mean “something of no current value,” specifically an advance in pay or other debt that had to be worked (“flogged”) off. [Second half of 1800s]

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Example Sentences

“But when you’re awake for too long, then the system gets overloaded. At some point, you can’t beat a dead horse. If you’re asking your cells to remain active for 30 percent more time each day, cells die.”

From New York Times

“I just let him go. You can’t beat a dead horse.”

From The Verge

Not to beat a dead horse, but it’s hard to ignore the uncertainty at cornerback and not have some concern that the team’s best-laid plan — free agent Ahkello Witherspoon being worth the $4 million guaranteed they gave him — has already blown up.

From Seattle Times

I can still hear my dad saying in his Oklahoma drawl: “Honey, don’t beat a dead horse,” so I divorced him.

From Los Angeles Times

“Out on the farm, we used to say, ‘Don’t beat a dead horse,’” he said and laughed.

From Seattle Times