After the old woman burns to death with her books, Montag returns home with one of her books that "fell into his hands." He sees this not as an act of theft, but of something his hands themselves did without his conscious instruction. He speaks with his wife and experiences fear and doubt.
The first important conclusion Montag reaches is that he feels no substantial connection to his wife. She goes to the bathroom and takes sleeping pills, and he tries to think of what he would do if she died. He comes to the conclusion that he would not weep, because she and he are not truly connected. This in itself, coupled with her complete dispassion over their neighbor's death, brings him to tears.
The second important conclusion Montag reaches is that books are not simply a collection of words on paper, but the physical representation of the writer's life and experiences. Instead of being inanimate objects, powerful only to those who read, they are the equivalent of a person's life, distilled into a form one can hold, lend, and experience more than once. This revelation, compared with the intangible TV walls and short attention spans of the world's inhabitants, brings him to wonder if there is any underlying truth in the rest of the world.