Flogging a dead horse is an idiom that means a particular effort is a waste of time as there will be no outcome, such as in the example of flogging a dead horse, which will not cause it to do any useful work.

What does beating a dead horse come from?

The origin of the expression 'beat a dead horse' comes from the mid-19th century, when the practice of beating horses to make them go faster was often viewed as acceptable. To beat a dead horse would be pointless, as it wouldn't be able to go anywhere.

Is beating a dead horse a bad phrase?

There is an old saying that we have all heard at one time or another, "You are beating a dead horse." ... You are beating a dead horse when you insist on talking about something that has already been discussed, a decision made and no amount of talk in the future will change the decision or the outcome.