If Charlie were sending text messages instead of writing letters, they would probably consist of a lot of frowny-face emoticons. That is, if he could even bring himself to text. In The Perks of Being a Wallflower, Charlie tends to straddle that fine line between sadness and depression. His solution: to totally withdraw himself from all social interaction. Sometimes he even turns to drugs.
Sure, Charlie has moments of joy and happiness, but even when he isn't spiraling into a deep hole filled with panic attacks and depression, there's a fog of bummer surrounding him. Bottom line: this guy sure knows how to bring himself down.