Poseidon is the reason the Odyssey takes ten years instead of ten weeks. When Odysseus blinds the cyclops Polyphemus — Poseidon’s one-eyed son — he doesn’t escape the consequence by being clever. He compounds it by shouting his real name back across the water as he sails away. Tell them it was Odysseus, son of Laertes, sacker of cities, of Ithaca.
Polyphemus prays. Poseidon hears.
For the rest of the poem, the sea is not just a setting — it is a god with a grudge. Storms, shipwrecks, sirens, Scylla, the loss of every man Odysseus sails with. Poseidon cannot kill him outright (the Fates have decreed nostos) but he can make sure Odysseus arrives home alone, broken, on a borrowed boat.