What do you find out when you steal your little sister's diary? C'mon, we know you've done it at least once! All of her personal, private thoughts and opinions, right? Well, that's what we're getting when we read Paul's journal, too. (Well, not your sister's thoughts—Paul's). Since he's the one telling the story, we can only hear his thoughts, but there sure are a lot of them—definitely enough to give us a very clear view of what Paul is like as a character.
One of his main character traits is the fact that he feels overshadowed by his brother. Check it out:
I thought to myself, OK, here we are. How long did it take Dad to get to his favorite topic, the Erik Fisher Football Dream? I'd heard it all before. Too many times. And I was about to hear it again. I tried to head him off by asking him something, anything, but he was too fast for me. (1.1.50)
Of course, Paul's thoughts also tell us something about the other characters, like his dad and brother. This passage tells us all we need to know about Mr. Fisher—and it's not too good.
Thank goodness for all the dialogue, or we might get bogged down in emotion. Dialogue is one of the main ways we get to know the characters other than Paul—like, for example, Erik and Arthur. When Joey comes over to Paul's house a little while after his brother is killed by a lightning strike, in which most of his hair is singed off, Erik starts making fun of him:
"Hey, check it out. It's Mohawk Man's brother."
Arthur stopped and started at Joey. He answered on their cruel wavelength. "I didn't know Mohawk Man had a brother."
'Yeah you did, butthead. The shoes! He was trying to take Mohawk Man's shoes!'
The two of them started to laugh. Erik said, "It's the hair that fooled you. No family resemblance.
Arthur picked up the banter. "No. No resemblance. None at all." (2.3.7-11)
When you hear someone saying stuff like this, you know you've got some bad guys on your hands. Paul's mom, while not evil like her oldest son, is also easily characterized through her speech. Her all-consuming concern with appearances is obvious from the things she talks about.
Look at the mailbox on that Tudor. That's not a Tudor-style mailbox. […] Those regulations are serious. […] (I)f twenty more houses decided to put up twenty different styles of mailboxes, it'd start to look like a shantytown around here. […] This is not a joke to me. (1.8.8-13)
Oookay, so matching mailboxes are a big deal to Mrs. Fisher. Weirdly enough, stuff like that tells you a lot about a person. Like, maybe she should be paying a little more attention to her sons and a little less attention to her neighbor's mailbox.
Here we are at the big one. Actions speak louder than words, right? So, Arthur killing someone based on Erik's orders tells us a little something about what kind of character he is? Oh yeah.
Erik […] turned to Arthur and said, "We may have a situation on our hands, Bauer."
Arthur starts to walk slowly west. His hand fumbled inside his gym bag. […]
Luis held his long arms out […]. "Why don't you come over here and try to smack me?" […]
Arthur reached Luis, turned, and whipped the blackjack around with a loud whack against the side of Luis's head […] Arthur stuck the blackjack back into his gym bag and continued walking, as if nothing had happened. (3.2.49-56)
He never said a word, and he didn't need to, for us to be able to see how messed-up, creepy, and cruel he is.