Vladimir and Estragon, the two protagonists in Waiting for Godot, spend most of the play waiting for the arrival of the eponymous Godot. Any value that their lives have seems to be bound up with the expected arrival of Godot. Therefore, the fact that Godot never arrives renders their lives valueless.
When the boy, sent by Godot, tells them that Godot "won't come this evening" as expected, Vladimir and Estragon immediately talk of killing themselves. Indeed, Estragon says to Vladimir, "Remind me to bring a bit of rope tomorrow," the implication being that they will hang themselves with that rope. Whatever purpose, meaning, and value their lives might have, Vladimir and Estragon seem to invest in the character of Godot, much as some people attribute meaning and purpose to God. With Godot, as it were, out of the equation, Vladimir and Estragon's lives are devoid of any meaning or purpose, as might be the lives of those who believe in God, should God be taken out of the equation.
Throughout the play, there is a recurring motif of nothingness. Vladimir and Estragon repeatedly lament that there is "nothing to be done." At one point in the play, Estragon comments that "nothing happens," to which Pozzo replies, "You find it tedious?" Estragon in turn replies, "Somewhat."
This exchange seems to nicely encapsulate the view of life that runs throughout the play, namely that life is full of tedious nothingness—there is no meaning, no purpose, and no value. A little later, Estragon repeats the same idea when he proclaims that "nothing happens, nobody comes, nobody goes, it's awful!" In total, as if to emphasize the point, the word nothing is repeated twenty-eight times in the play.