Seriously, this is not your own answer , just only copies from >>>

> The Black Door in Falkreath asks, "What is the music of life?" with the correct answer being: Silence, my brother. Answering incorrectly results in the door replying, >>> "You are not worthy". <<< The correct response is not an option until the Dragonborn learns it during either the "Destroy the Dark Brotherhood" or "With Friends Like These..." quests.

> The Black Door in Dawnstar asks, "What is life's greatest illusion?", to which the correct answer is, >>> "Innocence, my brother." <<< learned during the quest, "The Cure for Madness."