In Ray Bradbury's Fahrenheit 451, Guy Montag's greatest dilemma is continuing to exist in his government-controlled society after realizing that his life has no purpose—and that his job supports every lie society has taught him.
A third-generation fireman, Montag has been burning houses and books for ten years without ever questioning why he does so. Clarisse McClellan, a young neighbor, begins sharing her observations of the world, and asking Montag questions about his life—things that change the way he perceives himself and the world in which he lives.
One evening the firemen answer a call for 11 No. Elm Street. There they find a woman in her home, surrounded by books. As the firemen begin to soak the volumes with kerosene, Montag tries to get the woman to leave so that she will not be harmed when the burning begins.
"You can't ever have my books," she said. [...] The men glanced back at Montag, who stood near the woman.
"You're not leaving her here?" he protested.
"She won't come."
"Force her, then!" [...]
Montag placed his hand on the woman's elbow. "You can come with me."
"No," she said. "Thank you, anyway..."
"Please," said Montag... "Here." Montag pulled at the woman.
The woman replied quietly, "I want to stay here."
Beatty calls out numbers in warning, intent to start the blaze; the woman tells him to cease his countdown.
She opened the fingers of one hand slightly and in the palm of the hand was a single slender object.
An ordinary kitchen match.
In that moment, the men rush out of the house; and the woman ignites the match and dies as her house and books burn around her.
This is, to my mind, the pivotal moment of the book—the one that changes Montag forever. He has already had questions racing around in his mind about his job, his life and society (because of discussions with Clarisse), but this experience shakes him to his core.
When Montag finally returns home, he feels as if he has been poisoned, and it is spreading through his entire body. The source of the danger is the book that he stole from the woman's house when no one was watching. The "poison" is actually his awakening to knowledge, which has been kept from him and other members of society. He is now aware that something about books has been hidden from him: for why else would a woman choose to die rather than leave her books? But with this awakening, Montag is, in that moment, uncertain of everything.
[Montag] lay far across the room from [Mildred], on a winter island separated by an empty sea... Montag said nothing...he felt her move in the room and come to his bed and stand over him and put her hand down to feel his cheek. He knew that when she pulled her hand away from his face it was wet.
This experience so changes Montag that he does not want to return to work.
When Beatty, his boss, comes to visit, it seems the other man is suspicious of Montag. Guy now must be constantly on guard not to give himself away by something he says, most especially at work. At the same time however, Montag becomes reckless in his speech and behavior around Mildred's friends. At one point, he forces Mildred to listen as he reads to her, although she wants no part of it. Perhaps worst of all, as Montag begins to view the world through his altered perceptions, he is alone with no one to listen to him or guide him. Clarisse is gone, and Mildred remains unchanged.
Ultimately, Montag seeks out Faber (the former college professor) who lets Montag know where the power of books really resides. This will give Montag new direction and the resolve to change the path he has been on—he is newly committed to rebuilding society and protecting the knowledge held within books.