Poe's use of unreliable narrators, dark and gothic imagery, and psychological themes all contribute to the sense of uncertainty and horror in his stories. Additionally, his use of suspenseful and eerie settings, such as decaying mansions and remote castles, further heightens the sense of dread and unease experienced by the reader. Through these elements, Poe creates an atmosphere of tension and fear that keeps the reader on edge and adds to the overall sense of horror in his works.