Piranesi's amnesia makes him an unreliable narrator. While he seems to be a master of objective observation, his perception of reality is skewed by his inability to remember his own identity and the existence of the outside world. Take, for example, this journal entry titled "Do trees exist?" In it, Piranesi speculates on the origin of a leaf:
Many things are unknown. Once [...]I saw a bright yellow speck floating on a gentle Tide beneath the Fourth Western Hall. Not understanding what it could be, I waded out into the Waters and caught it. It was a leaf, very beautiful, with two sides curving to a point at each end. Of course it is possible that it was part of a type of sea vegetation that I have never seen, but I am doubtful. The texture seemed wrong. Its surface repelled Water, like something meant to live in Air.