"My fault, father," the cool clear prince replied,
"the blame’s all mine. That snug door to the vault,
I left it ajar – they’ve kept a better watch than I.
Go, Eumaeus, shut the door to the storeroom,
check and see if it’s one of the women’s tricks
or Dolius’ son Melanthius. He’s our man, I’d say."

– Homer

The Odyssey, Book 22, lines 162-164. In the battle with the suitors, Telemachus admits to forgetting to lock the door to Odysseus’ storeroom of weapons. With the help of the goatherd Melanthius the suitors were able get a hold of weapons as a result. Telemachus displays maturity and a sense of honor when he owns up to his mistake.