In "Fahrenheit 451" after Captain Beatty visited Montag at his home, what decision finalized in Montag's mind?
Montag is even more confused after Beatty leaves. He is restless and pacing, and tells Millie,
"I don't know what it is. I'm so damned unhappy, I'm so mad and I don't know why...I might even start reading books...I'm going to do something big."
So, he has an anxious feeling; he is unhappy and wants to do something about it, but isn't sure what yet. He gets down all of the books that he had hidden and decides to start there. He says, "I want to look at them, at least look at them once." He decides to break the law, to fly in the face of what Beatty has said about books being useless, and read. He hopes that books will help him to figure out "just one little thing out of a whole mess of things". So, he spends the entire next day reading. He takes Beatty up on his subtle offer to let him read for 24 hours, and tries to pack in as much reading as he can. Unfortunately, Millie is a bit stubborn, whiney and reluctant as he tries to drag her into it, and he gets so frustrated with her and her friends that he leaves to find Faber. Faber has what he is looking for though, and together they do indeed plan something big: outright rebellion against the law. But it all started with Montag's decision to read being finalized after Beatty left his house. I hope that helps; good luck!