The theme is that you sometimes need to step out of your comfort zone and not worry so much about others over yourself
Throughout the book, Charlie learns about how he needs to step out of his comfort zone and be less of a wallflower, whether it is through being told or experiencing what happens when he is a wallflower. At Charlie's first party, Sam focused more on protecting Charlie and got mad at Bob for giving Charlie a weed brownie, but later it seemed that Patrick blamed Charlie for being a wallflower, although not in a mean way. Then, Patrick pointed at me, and said something to Bob.'He's something, isn't he?'Bob nodded his head. Patrick then said something I don't think I'll ever forget.'He's a wallflower.' (25 PDF)This helped Charlie realize that he needed to make his own decision to do what was right for him.
There are a couple of points in the middle of the book where Charlie decides not just to be a wallflower. One of which is when he kisses Sam rather than Mary Elizabeth, causing him to not be allowed to talk to his friend group anymore. This went on until he stood up for Patrick and helped him fight Brad. Brad was using a homophobic slur and everybody was laughing at Patrick, but instead of ignoring it or laughing as well, Charlie decided to fight Brad. After the fight started and a bunch of people were fighting with Brad, Charlie decided to do what was right, rather than blend in. That's when I got involved. I just couldn't watch them hurt Patrick even if things weren't clear just yet. After this, he is allowed back into his old friend group with open arms, and they are proud of him. This taught him that it is best to do what is right rather than what is popular. This time period was good for advancing this theme because homophobia was an even bigger issue than it is today. Homophobia was used as a common view that Charlie disagreed with, and stood up against, which was rare given the setting.
The conflict here was that Charlie only had a few friends and never focused on how he felt. He just 'put on a mask' so he would fit in and look as normal as possible. This changed him in many ways. He started going to parties, drinking, and smoking, because most of the people around him did. He stopped caring about his health, and focused on being 'normal.'
Here, Charlie was going to graduation with some of his cousins. at this point, Charlie smokes quite often, but right at this moment he didn't want to. I went with all my Ohio cousins, who promptly pulled out a joint and passed it around. I didn't smoke any of it because I wasn't in the mood, and they said what they always say. Then, Charlie got bullied, but he didn't care. This shows progress from his past self because he doesn't care about fitting in; instead, he does what he wants. He may not realize his progress, but it happened and this moment proves it.