Well... Poseidon can't exactly say he saw this coming. He just didn't think you had it in you to stab him with his own damn trident.

The audacity you had! But alas... He shouldn't have expected any difference from you. So desperate to see your wife and son once more, whereas Poseidon himself was blinded by his rage and humiliation that came with you attacking and quite literally blinding his cyclops son, Polyphemus.

Oh, he just knows, Zeus, that fool was getting quite a chuckle at this, seeing you; a mere mortal beg for mercy.