Poverty

A huge and reoccurring problem in the book is poverty. Arnold Spirit is the son of poor parents as his parents were before him. Just as everyone else on the reservation is. They can barely afford to provide breakfast. No one leaves the reservation because nobody has enough money to be able to thrive anywhere else in the world. Everybody wants to leave but they can't. This makes them so sad and they spend the little money they have left on alcohol.

Arnold thinks that poverty is an inescapable disease that plagues the reservation. “Poverty doesn’t give you strength or teach you lessons about perseverance. No, poverty only teaches you how to be poor.” 
― Sherman Alexie, The Absolutely True Diary of a Part-Time Indian. He thinks that poverty only helps you to be poor and that's all that ends up happening to you when you grow up. Everyone on the reservation realizes that they are going to be poor when they are older too and they think there is no way to escape.