In Waiting for Godot, Lucky seems to be anything but lucky; he is a slave to the pompous Pozzo. Lucky must carry Pozzo's belongings, dance, and even think/recite on command. Otherwise, he seems more animal than man, waiting silently for orders and occasionally falling asleep, drooling, or attacking others that come too close to him. In the second act, Lucky serves a similar role, but he is unable to speak even on command, as he is "dumb."
One of the most notorious monologues in modern theater is Lucky's speech, wherein Lucky is commanded to "think." It takes the form of a several-minutes-long run-on sentence and mimics both religious preaching and philosophical professing. He begins his speech by discussing the existence of a personal god, but he describes this god as apathetic and, in many ways, impotent. As he continues his speech, it becomes a kind of frantic ranting, but he continues to use phrases such as "who can doubt it" juxtaposed with "for reasons unknown but time will tell," suggesting the incomprehensibility and futility of faith. His speech makes any sort of god appear to be a villain who plunges humans into fire and torment for no particular reason.
Some of the language in his speech also mocks academic and philosophical thought. His use of the word qua (meaning "by way of") over and over again suggests the pomposity and overuse of it in an academic sense, and he stutters when he refers to research in the "acacacacademy." It is worth noting that caca also refers to poop, a way to tear down the pristine image of the academy.
Lucky further refers to different researchers and thinkers throughout his speech, citing others, but he begins to refer to so many others that it becomes unclear what ideas should be attributed to whom. Similar to his use of the word caca, two of the scholars he cites are Fartov and Belcher, which suggests a lot of hot air or flatulence—again as a way to make fun of scholarship and philosophy.
In the end, Lucky may symbolize a lack of faith in both God and reason. He may, in fact, be "lucky" in the capacity that he never has to think for himself, instead following orders from Pozzo and otherwise standing mute. When he is commanded to think, he becomes frantic and confused.