In Book 17 of Homer's Odyssey, Odysseus finally returns to his home after being away for 20 years. Some readers wonder why Odysseus does not tell Penelope immediately that he is home.
One reason for this has been set forth from the beginning of the poem, namely the fate of Agamemnon. From the first book of the epic, the audience has been reminded that when returned home from Troy, he was murdered by Aegisthus and Agamemnon's own wife, Clytemnestra. In Odyssey 11, Odysseus even encounters the spirit of Agamemnon, who recalls what he suffered at his wife's hands, but who also suggests that Odysseus' wife Penelope is not the sort of woman who would do such a thing.
Still, Odysseus has travelled much and has been tricked on more than one occasion, so he wants to be careful. Even in Odyssey 19, when Odysseus and Penelope converse, Odysseus is disguised as a beggar and tells Penelope a fictional story, although this story does offer hope to Penelope that Odysseus is still alive.
So, Odysseus does not reveal his true identity to Penelope until the time is right because he wants to make sure that Penelope is not a second Clytemnestra.