Montag is a flawed character because he accepts his role at first, and then makes mistakes when trying to change who he is.
At the beginning of the book, Montag is satisfied with his life as a fireman. He says burning books is “a pleasure.”
With the brass nozzle in his fists, with this great python spitting its venomous kerosene upon the world, the blood pounded in his head, and his hands were the hands of some amazing conductor playing all the symphonies of blazing and burning to bring down the tatters and charcoal ruins of history. (Part I)
It does not bother him that his job is to burn books. It does not seem to affect him that he lives in an empty society. He does not question.
Montag has an epiphany when he meets a young woman named Clarisse. She tells him she is crazy, and points out that people in her family are often in trouble with the law for doing things like driving slowly and sitting and talking to each other. Most people do not do these things in Montag’s world. Everyone rushes from place to place and watches TV.
When Clarisse asks Montag if he is happy, the question baffles him at first. He begins to see the holes in his life. He wishes for something more.
The impetus for change is when Montag sees a woman burn herself up with her books. He wants to know what is in those books to make her do that. He steals some and takes them home, starting a chain reaction that ultimately leads to his altercation with his boss Beatty.
Montag finds out that his wife put in an alarm on him. He feels betrayed. Beatty scoffs at him and insults him, and this angers Montag more. He does not want to get arrested, and responds by turning the flame thrower on Beatty.
And then he was a shrieking blaze, a jumping, sprawling, gibbering mannikin, no longer human or known, all writhing flame on the lawn as Montag shot one continuous pulse of liquid fire on him. (Part III)
Montag is on the run. He finds the secret society of book lovers Faber belongs to, and slowly learns how to memorize books to save society. He has found her true calling.