Insanity is a common theme among short stories. The main character in "The Cask of Amontillado" is a socio-pathic murderer, where the author uses language to hint at his condition, but does not explicitly say one way or another whether the protagonist is suffering from insult or something deeper. In "The Yellow Wallpaper," Charlotte Perkins Gilman has the narrator write in a first person perspective to help shape the plot into a progression of insanity.
In the beginning, the character writes clearly and comprehensively about being ill. However, she neglects to specifically say what it is she is suffering from other than "temporary nervous depression." Taking this condition into consideration, it is easy to see how being quarantined and prevented from being active and participating in healthy, creative activities can actually hinder or reverse the healing of the main character rather than help her.
The most obvious example of how the character transforms into insanity can be seen with the way she talks about the wallpaper. In the beginning, she innocently describes the wallpaper as,"It is stripped off- the paper- in great patches all around the head of my bed, about as far as I can reach, and in a great place on the other side of the room low down. I never saw a worse paper in my life. One of those sprawling flamboyant patterns commiting every artistic sin" (Gilman). By just describing the wallpaper, the reader can see that she has not quite become obsessed with paper, only just interested by it. Later on in the story, the narrator says,"There are things in that paper that nobody knows about but me, or ever will. Behind that outside pattern the dim shapes get clearer everyday. It is always the same shape, only very numerous. And it is like a woman stopping down and creeping about behind the pattern" (Gilman). Obviously, the narrator has become entirely obsessed by the pattern and is now imagining that she's seeing things behind it. After only a few weeks, she has descended into madness, due to a hideous wallpaper arrangement.
The protagonist's intrigue with the wallpaper is not the only way Gilman displays the oncoming insanity. She also effectively uses language with the writings of the main character. Talking about how she sees a woman creeping about by daylight, the narrator goes on to say, "I always lock the door when I creep by daylight. I can't do it at night, for I know John would suspect something at once" (Gilman). A direct relationship can be seen by the woman creeping outside and the narrator herself creeping about. She has not quite come to terms with herself yet that she is the actual person that is doing the crazy things and creeping around the yard.
In the end, however, the transition is more than obvious. The husband walks in to find his wife crawling about the room with her shoulder against the wall, "I kept on creeping just the same, but I looked at him over my shoulder. 'I've got out at last,' said I, 'in spite of you and Jane! And I've pulled off most of the paper, so you can't put me back!"(Gilman). By "getting out," the narrator has officially broken through the barrier of sanity and had the realization that she is actually insane.