Why is Polyphemus surprised by the fulfillment of the prophecy?

Polyphemus is surprised by the fulfillment of the prophecy because he underestimates the cunning of Odysseus and believes his own strength and isolation make him invulnerable. The prophecy, which foretells that he will be blinded by a man named Odysseus, seems implausible to him, as he is a formidable giant. Additionally, he dismisses the warnings from his father, Poseidon, and is caught off guard when Odysseus cleverly executes his plan. This underestimation of both Odysseus and the power of fate leads to his shock when the prophecy comes true.