Arnold is a funny, funny guy and cracks jokes – or draws hilarious pictures – even at his darkest moments (See, for example, figure 12.4, figure 24.5, and figure 27.2). Sherman Alexie has said that "being funny breaks down barriers between people. I can get up in front of any crowd, and if I make them laugh first, I can say almost anything to them" (source). We think this applies to Arnold most definitely.
Arnold is a teenage boy who is just packed full of words and images and ideas and thoughts and feelings. As we see from the novel's first few paragraphs (1.1-1.5 in which he compares his brain to a car engine with too much brain grease and a French fry drowning in a deep fryer), Arnold has about a million different metaphors for every situation. As a character, he's what we might call hyperbolic (or exaggerated). Is this a bad thing? No way. A lover of words, Arnold likes big gutsy images and huge exuberant ideas. Sure he's a little over the top – but that's why we love him. Arnold, much like his writing, is filled to the brim with life.
Here's the thing about Arnold – even though he goes through a massive amount of crap in his life, he is writing is almost always hopeful. He's always filled with joy, he always is excited to be alive. Take his joy lists, for example in Chapter 24. In order to cope with all of the death in his life, Arnold makes lists of his favorite foods, books, bands, and basketball players. Arnold's hope gives him buoyancy – and is what ultimately leads him to fight for his dreams by leaving the reservation.