Montag and Preston are both confronted with individuals who lead them to mental and emotional clarity.
After Montag and Clarisse are walking together, Montag "tilted his head back in the rain, for just a few moments, and opened his mouth"(24). Clarisse's unique personality intrigued him and after meeting her, he began trying new things. In this situation Montag copies what Clarisse previously did to see what it would be like. He is now beginning to think for himself instead of blindly following the government and living his life unhappily. Similarly, when Preston is interrogating Mary, she asks him "why are you alive?" He begins to understand he has a duty and was put on Earth for a reason, and it is not to serve the government. The main reason he was put on Earth is to feel, otherwise he is not really alive. He now understands that anything without feeling is not really anything at all so he takes Mary's advice. Preston and Montag would still be the same people if they had not met Mary and Clarisse.
Additionally, both Montag and Preston have similar turning points in their thoughts toward the government. When leaving the burning woman's house, Montag's "hands had done it... turned thief. Now it plunged the book under his arm, pressed it tight to his sweating armpit"(37-38 Bradbury). Be blames his hands to give the reader an idea of the conflict between his mind and body. He never wanted to take something so badly, but his mind knows the consequences he could be in. Eventually his body wins and his hands, not his mind, end up stealing the book. Likewise in Equilibrium when Preston accidentally breaks his interval of Prozium, he begins to feel and his emotions takeover him when he cries. He is confused as to why he felt the way he did, he is crying but at the same time he is overjoyed. He is feeling a catharsis for the first time and does not know if he is happy, mad, or sad. After this exotic experience, Preston stops taking his interval of Prozium. Without going through these experiences Montag and Preston could still be working for the government.
Montag and Preston's initial beginnings and mindset, their ways of solving their conflicts, their interactions with other characters, and their questioning of authority make it seem as if the two characters are were created solely to be alike in two separate settings. And not only are the two characters similar but almost all aspects of the two stories are alike. If Clarrise was in Equilibrium and Mary was in Fahrenheit 451, the endings would be similar if not exactly the same.