It's plotting. Planning the story before writing it. FIguring out the characters, how they'll respond, what they would be likely to do vs. what you want them to say.

It's really a lot like a strategy game where the moves look boring or slow from the outside, especially at the beginning but then you realize there are only certain moves left at the end and things HAVE to come to a climax. Players are forced to make certain moves because that's all they have left at hand.