In Fahrenheit 451, there are a number of events and characters which contribute to Montag's change. Here are some examples:
Clarisse McClellan: Montag's sixteen-year-old neighbor is unlike anybody else Montag has ever met. In their first meeting, her question to Montag ("Are you happy?") prompts him to start questioning his chosen profession and his values.
Mildred's attempted overdose: When Montag's wife tries to kill herself, Montag is horrified by the attitude of the two men who treat her. He is particularly shocked by the fact that Mildred appears unable to recall what happened when she wakes up the next morning and flatly denies that she would do something as "silly" as take all of her pills. This event leads Montag to realize that people in his society are both empty and disconnected.
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