What does Will insist to the reader directly after he introduces himself in the beginning of Chapter One? Why does he say he does this?

Will insists to the reader after he introduces himself in Chapter One that the story he is going to tell is true, even if the reader thinks he is making it up or “losing it” (1,2). He insists that this happened to him. He says he is saying this because “don’t nobody believe nothing these days” (1-2).