What final question does Clarisse ask Montag on the night of their first encounter? Why is this question important?

Clarisse asks Montag the simple question, "Are you happy?" Montag does not know how to answer this question at first. Clarisse stirs a depth of emotion that Montag is not used to. It is only after she leaves that Montag realizes that he is deeply unhappy. The burning of books begins to feel like temporary highs followed by crushing lows. This just has become Montag's life. He goes home to his loveless marriage to find Mildred, his wife, has overdosed on sleeping pills.