Answer:
Odysseus tells the Cyclops his real name.
Step-by-step explanation:
After tricking the Cyclops into believing that his name is Nobody, so when they blind him and he asks for help when the other cyclops ask him, Who attacked you?, Who blinded you?, he would answer "Nobody", they escape and Odysseus from the sea tells him that his name is Odysseus, this is a foolish thing, because the cyclops could seek vengance for what he did to one of their own, and the only reason to reveal his real name is so people would know it was him who did it and taking all the credit.