Montag is radicalized into rejecting his profession in a series of slow realizations, in which he begins to connect the dots of his life and how unhappy he is. Clarisse is the catalyst that starts him on the journey; her appearance in his life is quickly followed by Mildred's suicide attempt. He starts to come alive emotionally and to question his society's values, which he realizes have left him empty and unsatisfied.
The turning point comes as he participates in a book burning in which the owner of the books, an older woman, commits suicide by burning herself up rather than living without her books. Montag comes home stunned and changed:
His hands were ravenous. And his eyes were beginning to feel hunger, as if they must look at something, anything, everything.
He has a book he has stolen from the woman's house in his hands. At this point, he no longer wants to go to work. He no longer enjoys book burning. He asks Millie to call Beatty and tell him that he (Montag) is sick. All of this is part of his metamorphosis into a new person. He tries very hard to explain his reasoning and his experience to Mildred, but she is completely conventional in her thinking:
"Mildred, how would it be if, well, maybe, I quit my job awhile?"
"You want to give up everything? After all these years of working, because, one night, some woman and her books—"
"You should have seen her, Millie! "
"She's nothing to me; she shouldn't have had books. It was her responsibility, she should have thought of that. I hate her. She's got you going and next thing you know we'll be out, no house, no job, nothing."
"You weren't there, you didn't see," he said. "There must be something in books, things we can't imagine, to make a woman stay in a burning house; there must be something there. You don't stay for nothing."
It is the fact that the woman was willing to die for her books that has such a profound impact on Montag. He realizes there must be something of great value in books.