The projection of mental states can be a powerful tool in the influence of fright in the mind of a reader. As Franklin Delano Roosevelt once said, "there is nothing to fear but fear itself". If this is such, nothing could be worse than a projection of one's own fears into reality. Poe believed that the worst occurrence one could endure was mental disintegration. Should this be true, than the projection of a man's disintegration would incite the greatest fear of all. Roderick Usher himself was suffering from this. He is constantly referred to as a "hypochondriac"(269), and was suffering from "an acute bodily illness - of a mental disorder which oppressed him"(264), as if to say that it was the incarnation of his mental condition that was causing his physical illness. One can chart his degradation by the condition of the house. It is explained that "the physique of the gray walls and turrets, and of the dim tarn into which they all looked down, had, at length, brought about upon the morale of his existence"(268); he saw his own mental state in the house, and was horrified by it. The house itself was in detestable condition; the demeanor of the house was an "indication of extensive decay"(265), just as Roderick's body was. It was, however sturdy, with the exception of the fissure down the center of the house, dividing it into two, just as Roderick's mind was divided - between his personality and that of his sister. Eventually, as his two personalities confront each other, culminating in the death of both, and resulting in the fissure collapsing - showing that it was the disorder itself that caused his death (his other personality killed him), and thus showing the ultimate mental projection (physical events occurring).
Mental deterioration can be shown in the narrator himself. In the beginning of the story, the narrator becomes so disturbed by the condition of the property itself, he invents the entire occurrence of the house and its contents.