Montag is a "fireman" in a futuristic dystopian society where his job is destroy books in order to promote societal harmony. While the government ultimately enforces this total censorship of the written word, it was in fact the citizens in this society who initiated literature's downfall.
As people became more entranced with television programming (Mildred Montag, Guy's wife, watches TV nonstop), they began to be irritated by books, which were simultaneously taxing to understand and controversial. They asked the government to get rid of them, and the government happily complied.
Montag had always accepted this as a status quo and enjoyed his work until little things began to eat away at him -- his neighbor Clarisse, a free-thinking teenager, disappeared, allegedly killed by a hit-and-run. A woman refused to leave her burning house and abandon her books. His drug-addicted wife overdoses, and he watches how indifferently go about reviving her, as if she is a car to be fixed, not a person of value.
Then one day, Montag accidentally picked up a book to be burned and read one line out of it. And that's when Montag decides to start collecting books.
(If you haven't read Fahrenheit 451, go do it. I'll wait. If you're not a science fiction fan, don't worry, you'll still like it. And whatever you do ... don't watch the movie(s). They're the worst.)
"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."