That's how you write novels actually. You suddenly hit upon something and you realize this is the path you were meant to take. You'd be a fool if you didn't follow it. Perhaps it's like solving a difficult question in pure mathematics. There must be a moment when the solution is so simple and evident that you wonder why you hadn't come upon it before. When you do come upon it, you know it in the deepest part of your being. It carries its own logic.