Guy Montag has been a fireman for ten years.
Fahrenheit 451 is a novel about independence of thought, and the exposition of its narrative clearly presents the lack of worthy thoughts that Montag's wife and so many others display in a futuristic society. Though Montag has been stealing books for years, it is his unexpected encounter with Clarisse McClellan, whose face contains in it a "gentle hunger that touched over everything with tireless curiosity," that causes him to begin seriously questioning his society. Then he comes to realize how he has lost a part of his humanity.
After the curious Clarisse asks Montag if he ever reads any of the books that he burns and if he is happy, Montag is shaken. "What a strange meeting on a strange night," he remarks as he walks home. He marvels at how strong Clarisse's sense of self-identity is. Clarisse's power contrasts sharply with the personalities of Montag's wife, her friends, and many others.
It is at this point that Montag's life begins to change; he has had his natural instincts, so long repressed, now piqued.