In Book 9 of The Odyssey, why does Poseidon curse Odysseus for blinding his son, Polyphemus?
The Cyclops, Polyphemus, was a bad host to Odysseus and his men. According to the ancient Greek rules concerning hospitality, Polyphemus ought to have made them welcome and given them food and shelter and even gifts. The ancient Greeks believed that Zeus protected all travelers, and so to honor them was to honor him; likewise, to harm travelers was to dishonor him. When Polyphemus eats Odysseus's men, arguing that he need not obey the gods because he is stronger than they, Odysseus is forced to find a way to escape the monster. He even believes that Zeus would find his violent action permissible given the circumstances. So, Odysseus and his men blind the Cyclops after getting him quite drunk, and they make their clever escape tied to the bellies of sheep when the monster rolls the stone away from the door to let his herds graze the next morning.
However, Odysseus had lied earlier about his name, telling Polyphemus that his name was "Nobody" so that when other Cyclopes came to his aid, he could only tell them that "Nobody" was hurting him. Once he has reached his ship and, he believes, safety, he taunts the monster, telling Polyphemus his real name so that the monster will be able to tell others who it was that bested him. The problem? This also allows Polyphemus to tell his powerful father, Poseidon, god of the seas, who has harmed him, and since Odysseus must travel the seas to get home, his pride is really responsible for making his journey longer and more difficult than it otherwise would have been. Poseidon tries to exact revenge on Odysseus for blinding and humiliating his son, Polyphemus, the Cyclops (who, frankly, sort of deserved it considering his disregard for the rules of hospitality).
When Odysseus visited the cave of Polyphemus, he found out that Poseidon was his father. From that point on, he should have watched his words. However, he made a huge mistake. Once he and his men escaped the Cyclops's cave, he never should have yelled back at Polyphemus and given him all of his information. He told Polyphemus his name, his father's name and the name of his home land. He wanted Polyphemus to tell all who he encountered that Odysseus was the mortal who tricked him and blinded him. He did those things to escape with his men, but he took it one step too far when he became boastful. Had he kept his mouth shut and remained humble, he would never have incurred Poseidon's wrath.