In the play, the line is attributed to Estragon, who declares that he was beaten up for spending the night in a ditch. Estragon is speaking to Vladimir, and the line can be found at the beginning of act 1.
Beckett doesn't reveal who beat up Estragon, however. Yet, it does appear from the text that Estragon's encounter with the nameless thugs is familiar. When Vladimir asks Estragon whether it was "the same lot as usual" who beat him up, the latter merely says that he does not know. This troubling, quizzical response tells us nothing; therefore, there is only uncertainty surrounding Estragon's unfortunate mishap the night before.
Estragon's type of reply, however, is the norm throughout the play. Both Estragon and Vladimir ask many questions of each other, but neither can provide definitive answers to those questions.
Vladimir maintains that Estragon would be "nothing more than a heap of bones" without him. Next, he mysteriously says that "it's too much for one man." However, Vladimir never explains himself. We are led to wonder whether he is referring to the burden he carries as Estragon's protector or the troubles Estragon continually suffers.
For his part, Vladimir also mysteriously claims that he and Estragon used to be "respectable in those days." However, he is convinced that "it's too late" now. He blames those who "wouldn't even let us up." Again, there is uncertainty surrounding Vladimir's words. We are led to wonder why "it's too late" and who it is who has been keeping both men down.
The uncertainty surrounding Estragon and Vladimir's words is unsettling. We get the idea that both men share a secret language, one that we aren't privy to. Their conversation also highlights how little we truly understand others. Both Estragon and Vladimir experience difficulties in understanding and empathizing with each other. By extension, we also experience the same thing.
This utterance, like many others in this intriguing play, is a reference to the seemingly random acts of pain, violence, and injustice that Life brings to all of us, part of Beckett’s claim that Life, far from being a pleasant state, is a sort of curse, because we must all “crawl through the mud” of physical existence. In the play the line is a response by Gogo to Didi’s question about how he spent the night in a ditch. The pronoun “They” is intentionally without antecedent, as a way of expressing the nonhuman and therefore unattributable and unretaliated nature of all our “beatings," a part of our very existence. Often in our own lives we will experience an injustice or a physical condition bringing pain, and we vaguely ask “Why me?” and “I don’t deserve this.” These are the moments Beckett is referring when Gogo says “Certainly they beat me.”