"Beating a dead horse" is a colorful idiomatic expression that is sometimes employed when efforts to achieve a certain end are carried on even when it is clear that the desired end will never come to pass. The idiom can be applied to a wide range of situations, ranging from attempting to pass a course after missing too many sessions to attempting to revive a love interest that is clearly over. Even businesses may engage in activity that amounts to beating a dead horse by attempting to generate interest in a product that is now considered obsolete and will never again capture the attention of the buying public.
As with most English sayings, "beating a dead horse" helps to trigger a specific vision. In this case, the vision points to a situation in which changing an outcome is completely futile. In the days when horses were used as a main means of conveyance, using a whip to urge a horse to keep going was sometimes common. People foolish enough to not realize when a horse had expired would sometimes use the whip or strap in a fruitless effort to rouse the horse. If the horse was in fact dead, all the effort expended in the use of the whip was completely non-productive.
Many people still engage in beating a dead horse of some kind or another. For example, continuing the romantic pursuit of an adored one even after the object of affection has made it very clear that he or she is not in the least interested can be seen as an exercise of futility, wasting time and resources that could be diverted to finding someone more open to the advances. Attempting to perform a task when the individual does not have the skills or aptitude necessary to learn the proper skills could also be seen as beating a dead horse, since the task will never be completed successfully. Typically, any situation in which no amount of effort will produce the desired outcome can be described using this particular idiomatic phrase.
Choosing to avoid beating a dead horse involves recognizing that any opportunity for success is now past, and the investment of any more time or other resources will only lead to waste and frustration. People who are able to accept that the outcome in question cannot possibly come to pass will often be in a better position to move on from the situation and find other activities or interests in which there is still some opportunity to enjoy success. For those who are unable to break away and keep applying time and resources to what is truly a hopeless situation, beating a dead horse can eventually lead to physical, emotional and possibly even financial ruin, with nothing left to show for the efforts.