In horror movies or novels, the thirteenth floor is unlucky for several reasons: 1. Building structure: The 13th floor is usually the top or highest floor of a building. Such a design often makes people feel insecure. In addition, if the structure of the building is poor or there are potential safety issues, then the people living on the 13th floor may also feel fear. 2. Legendary stories: There are some horror stories or legends about the 13th floor in some legends. These stories may have originated from people's prejudice, misunderstanding, or exaggeration, so they were used to create an atmosphere of terror. 3. Character setting: In some horror movies, the characters on the 13th floor are usually regarded as ominous places. These characters could be the curse of the building itself or the disaster caused by certain people or events. By setting the 13th floor as an ominous place, movies or novels could enhance the horror and tension of the plot. It should be noted that not all horror movies or novels described the 13th floor as an ominous place. In some movies or novels, the 13th floor might be an interesting character or a fascinating plot point.