When somebody is given a job that can never be finished they are said to have been given a SISYPHEAN TASK. This saying comes from Greek Mythology.
Sisyphus was the king of Corinth. And just like every Greek Myth there are multiple versions of what happened. The most popular myth is that he was punished for believing he was more intelligent than Zeus himself. He cheated death twice and Homer declared him, "the most cunning of men".
The first time he cheated Death, he somehow managed to chain up the reaper. This culminated in nobody dying and effectively everybody becoming immortal. However, Ares the God of War intervened and the natural order was sustained with mortals dying again.
The second time he deceived Hades by telling him that his wife was not performing the rituals and sacrifices properly and that if Hades let him return to the land of the living he would instruct his wife on how to perform the rituals properly.
Upon dying a third time, Zeus was most unhappy with Sisyphus' tricks and especially declaring himself smarter than Zeus himself. And as we all know it's not a good idea to insult the gods, especially the Olympians.
Zeus devised a punishment where Sisyphus had to push a large, heavy boulder up a hill all day, only to have it roll back down to the foot of the hill upon reaching the top. Sisyphus was locked into this unbearable job in the underworld for the rest of time.