Illiteracy as a running character gag
Charlie’s inability to read is more than a single embarrassing reveal. It keeps creating small, practical problems: written instructions, signs, and documents become obstacles, while the people around him can exploit or misunderstand that gap. The joke comes from watching an ordinary task turn into a crisis because Charlie cannot use the information everyone else takes for granted.
Why the joke fits the show
It’s Always Sunny in Philadelphia often builds comedy by letting its characters charge ahead with confidence despite obvious limits in their judgment or abilities. Charlie’s illiteracy gives that pattern a concrete form. He is not simply confused by one difficult text; he can be confidently wrong about what writing is doing at all. That mismatch between certainty and comprehension makes the gag easy to revisit in new situations.
His songs written in invented marks push the idea into visual comedy. They look, to the characters, like evidence of a private creative system, but the marks cannot serve as ordinary written lyrics. The audience can see the gap between Charlie’s sense that he has made something readable and what the page actually communicates.
A limitation that keeps generating plots
Because reading is woven into everyday life, the premise can recur without needing a new explanation each time. A note or form can become a source of confusion, a chance for another character to take advantage, or a reason Charlie invents his own workaround. The result is a durable joke: the obstacle is basic, but Charlie’s response to it is never merely basic.
