The quote "Circumstances are beyond the control of man; but his conduct is in his own power" by Benjamin Disraeli is clearly reflected in Ray Bradbury's Fahrenheit 451.
Guy Montag is a professional fireman: a man trained to burn books in a society that hinders the development of original thought and seeks to control the minds and actions of its members. At the novel's beginning, Montag does not question his place in the world: he burns books and cannot consider an existence beyond the one he knows. In fact, he enjoys it:
It was a pleasure to burn.
It was a special pleasure to see things eaten, to see things blackened and changed.
When he meets Clarisse McClellan the first time, she asks if he has ever read any of the books he has burned and he laughs, reminding her that it's against the law. This shows the reader that Montag has no control over the burning or saving of books: the law is clear about owning and reading books.
As we read, we learn that there are those who break this law and hide books in their homes. The first major event that shakes the way Montag views his job and society's laws is the burning of a house where its occupant, an older woman, is still inside. This has never happened to him before. It takes place when the fire company is called to 11 North Elm:
Always before it had been like snuffing a candle. The police went first...so when you arrived you found an empty house [...] ...tonight, someone had slipped.
Montag is amazed by the woman who refuses to leave her books.
You can't ever have my books.
As Beatty counts down in warning, the woman addresses him:
"You can stop counting," she said. She opened the fingers of one hand slightly and in the palm of the hand was a single slender object.
An ordinary kitchen match.
It is she that ignites her kerosene-drenched home and books, willing to die rather than live without her books. Up to this point, Montag's job had been just way to pay the bills: he was burning things that had no feelings, not people. He comes to realize he cannot go on being a fireman.
Clarisse changes him as well, asking Montag many questions that make him take notice of the world he has forgotten or has never seen: that there is dew on the grass in the morning, that the blurs he sees in his speeding car are really objects: cows, flowers, etc. Montag begins to notice a great deal. Then he begins to hoard books and even reads them—one time he reads aloud to his wife's friends. He meets Faber, a teacher who also hides books. Faber agrees to help Montag navigate his way out of the life he is living. Eventually, Montag will have to change his conduct.
Mildred turns Montag in, and his boss comes to burn their house down. To protect Faber from being discovered and to save his own life, Montag fights back—first he kills Beatty and then destroys the Mechanical Hound. In an instant, he is on the run. Montag is not able to change the world alone, but with the help of others of the same mind, he will be able to alter the future of society. As bombers destroy the only life he has known, Montag reaches the safety of the woods, where people like himself have found sanctuary. They move to join others who will rebuild society.
Alone, a man may not be able to change society (circumstances), but he can alter his actions (conduct), and when joined with others like him, he can change the world. Changing his conduct empowers Montag. His actions and those of others begin a revolution.