It creates an exaggerative voice, which affects the narrator’s credibility.
The narrator speaks with a great deal of hyperbole so as to add humor and interest. However, all of this over exaggeration makes it hard for the reader to know what is real and what is false. In actuality, the author Sherman Alexie based the book off events in his own life, so much of what is in the book is true. The story does not have a formal tone anywhere and the atmosphere is not gloomy. Sometimes the book has a depressive voice when he talks about difficult things but hyperbole does not create this.