In case you haven't figured it out yet, Charlie isn't exactly the most active participant in life. (The title of the book might have tipped you off.) On the rare occasion that Charlie does participate, he's not the most absorbent either; he's more of a dense rock than a porous sponge.
So where does he get his life experience from?
When he's at his most introverted, Charlie doesn't totally retreat from reality. Instead, he reads. A lot. He likes to read most books twice, too. His required-reading list is jam-packed with profound classics ranging from To Kill a Mockingbird to The Catcher in the Rye. And bonus: many of these books have young-adult protagonists just like Charlie.
At first, Charlie's a little lacking in the analysis department: "[To Kill a Mockingbird] is now my favorite book of all time, but then again, I always think that until I read another book" (1.4.2). Charlie's still learning that you have to back up statements like that with a why. (Shameless plug: Hey, Charlie: check out our other Literature guides. We've read a lot of the books you've been assigned.)
Maybe Charlie is spending too much time living vicariously through the novel's young protagonists to do any sort of critical thinking. Over time, though, with Bill's guidance, Charlie starts to think more critically about the novels he's been assigned and the characters within them. Bill advises him, "Try to be a filter, not a sponge" (4.6.10). We're pretty sure Bill also hopes Charlie will apply the same philosophy to his life, but Charlie's not quite that spongy yet.
Charlie's all about the classics when it comes to music, too. His letters are packed with references to music from the 60s, 70s, 80s, and early 90s, some you've probably heard of and others that will have you searching the iTunes store for samples. It's rare to finish a book with a song stuck in your head, but with Perks, it might just happen.
But here's the thing. Just like with the books, Charlie seems to be living vicariously through these talented musicians: "I think it would be great to have written one of those songs," he says (2.7.9). But he doesn't. At least not for now.