Beckett's Act Without Words is a silent depiction of futility. In the Greek tradition, the main character is facing an eternal punishment, forced to work at tasks which he or she will never be allowed to complete. The Greek myths of Sisyphus and Tantalus come to mind after reading Beckett's work. Sisyphus was punished for arrogance by rolling a boulder up a hill, but when it reaches the top it rolls back down again, for eternity. Similarly, Tantalus was punished by being made to stand in a pool with a fruit tree branch extended above him, never able to reach the fruit or touch the water forever. In much the same way Beckett's main character finds himself on a stage and is whistled at to complete tasks which may help him grab hold of a carafe of water but never allowed to grab hold of the carafe.
This story of constant frustration is a disturbing one, an idea that has tortured the minds of men for centuries, since the Greek philosophers. Is this person being punished? One could never know for certain as no outside information is provided for the readers beyond what the main character observes and does. With no end in sight, this person just has to respond to data and hope that he can do something right and be rewarded for it with water at last. He doesn't seem too concerned, however, showing more anxiety about the state of his fingernails than the perpetually receding water. Most likely, Beckett's point is to illustrate how people are thoughtless, more inclined to worry about the inconsequential than the necessary.
Another important aspect of this story to consider is the fact that the protagonist awakens upon a stage. He is trapped on a platform, denied exit by an unknown force. Something else besides himself exists as evidenced by the whistle, but for all he knows he may be the only being in existence. He's completely alone. Despite appearances, he may in fact be under observation by an audience as the stage seems to imply. This idea of endless, public punishment is one alluded to in an episode of the British TV show Black Mirror. Whether he knows it or not, the main character is potentially being watched by any number of people laughing at his frustration and torment. In a very real way, this is a commentary on human existence. We try and try at things that will never result in anything worthwhile, all the while trapped in the public eye as our brothers and sisters watch us fail. No matter what, we are always utterly alone.