Like most of Poe's works, it is important to remember that when the story is told in first person (by a narrator who is most often also the main character), it must be understood that character description is not only biased and one-sided, but often cannot be completely trusted. Poe is famous for his unreliable narrators, which contribute to his trademark mystery, horror, and gothic stories and themes.
The main character and narrator of "The Pit and the Pendulum" is a tortured prisoner of the Spanish Inquisition. Even before his ultimate imprisonment, he admits in the first line of the story that his mental clarity is leaving him:
I WAS SICK—sick unto death with that long agony; and when they at length unbound me, and I was permitted to sit, I felt that my senses were leaving me.
We can assume for the rest of the story that everything he describes (including himself) is filtered through his physically tortured and mentally weakened state.
Additionally, he is obviously frightened, not only by the fear of the unknown, but by the assumption that his death is imminent and just around the corner. At first, he is even to scared to open his eyes:
There I suffered it to remain for many minutes, while I strove to imagine where and what I could be. I longed, yet dared not to employ my vision. I dreaded the first glance at objects around me
However, despite his imprisonment and full bondage (so that only a hand is free to reach food), despite the physical and psychological torture he is fighting to overcome, and despite his fear, he is hopeful that he will be freed and remains strong enough to take account of his surroundings to be able to remember some of the details he recalls, and then to retell his story when he is freed at the end.