As a science-fiction novel, Fahrenheit 451 features some futuristic technology that seems unbelievable to us now. For instance, the firehouse "mascot," the mechanical hound with its poisonous needle nose, seems far from realistic. Also unbelievable is the hound's ability to track people who have forbidden collections of books. When Bradbury's novel first appeared, the concept of a TV wall probably seemed really unbelievable, but now-- not so much as our flat-screen television sets become larger and larger.
The actions of the characters in this society seem unbelievable in contrast to the way we live. Firemen set fires, instead of putting them out, and reading books is not only a bad thing, it is illegal and can be punished by death. Once Montag rebels and runs away, he joins "the wanderers," others in rebellion who have dedicated themselves to memorizing books so that their contents will not be lost. This idea is not realistic for us since we have so many ways to preserve documents and find it hard to imagine having to memorize books to save them.
The most realistic element in the novel is human nature, which does not change. We can easily identify with the emotions and beliefs of the various characters: fear, anger, depression, rebellion, conformity, self-preservation, moral idealism, and the determination to protect and defend personal freedom at any cost. This novel is very real indeed when we consider the characters and the choices they make.