In The Odyssey, what does Odyssesus learn from Agamemnon in the Underworld?

The voyage of Odysseus into the underworld occurs in Book
11 of this epic classic. In this book, Odysseus meets with a wide range of people,
ranging from his own mother to former comrades in the Trojan war. One of these, as your
question indicates, is Agamemnon. Agamemnon is quick to reveal the events that brought
him to be in the Underworld. Having returned to his home after being triumphant in the
Trojan war, Agamemnon was killed by his wife Clytemnestra. He also narrates how his wife
had killed the prophetess Cassandra. Agamemnon, having narrated his story, then goes on
to wish Odysseus luck in his voyage home, and expresses envy that Penelope does not
display the same treacherous characteristics as his wife did.