The Perks of Being a Wallflower is all of Charlie's letters in one book. This is the way the author wrote it so the reader knew it was from Charlie's point of view. The recurring element is the letter format. Charlie is writing his letters to you, the reader. When Charlie writes his letters, it is his way of letting out what he is going through. Him being able to write down what is happening to him, for him to realize it's not all a dream. Also as a precaution, like telling the reader to watch out and avoid what he had to go through. I think he writes these letters because he just needs someone to talk to and vent and won't have to know if the reader judges him. It's his way of letting his problems go and get them out of his head.
The major piece of irony in The Perks of Being a Wallflower is Aunt Helen. Charlie talks much about Aunt Helen, referring to her as his favorite person in the world. But significantly Charlie doesn't remember what she would do to him. Something bad happened to her when Charlie was 7, and whenever Charlie thinks about this it take him to a bad place. The title can also be referred to as irony. When he makes friends, they call him and themselves wallflowers. But the story doesn't necessarily point out the perks of it. The book talks about how bad things happen to all the characters.
When Sam kisses Charlie, it triggers something in Charlie which involved Aunt Helen. It made him somewhat remember being molested by her. But when he remembers this, he doesn't realize it was by Aunt Helen. After the kiss with Sam, Charlie has a dream of being molested by his Aunt Helen, but doesn't think it means anything. Until he is sent to a hospital after his breakdown. He is told the dream was a memory, and that is when he finds out about his childhood with Aunt Helen.