Despite the narrator's guilt over the situation, he is not to blame for his brother's death. He may have treated him with indifference and occasional malice, both of which are displayed by his words and actions in the story, but in the end, those words and actions were not the primary cause of Doodle's death. We as readers know that his condition is what eventually led to his certain death, and that from the very beginning, Doodle was supposed to have died many times before. The fact that he had lasted as long as he had was a fact of sheer amazement.