When you're writing a story, you usually have some sort of outline; be it an ARC, ABC, or 1.2.3. sort of outline, it sets up what happens, and when, to whom, and where as well as how it happens.
Now, you can take that outline and make a dozen different stories out of it just by varying ONE of those items.
From what he's said, Kris has the outline in place. He's using it to introduce situations that move sequentially toward a planned completion.
How he gets there is why it's called "Creative" writing, as opposed to setting up a menu. The outline keeps him oriented, and the fans give him ideas as to direction, but stories take on a life of their own and a momentum of their own and sort'a write themselves, with the author serving as the secretary to the action going on in his mind. That's the fun and scary part... And so far, PItW is going splendidly!