Knowing when to stop. How many details to add and when to stop the story. Just like in baking you know have a kitchen full of ingredients but you need to add just the right amount, the perfect combination and bake at the right temperature for the correct amount of time to make a good dish. Writing is the same. It's difficult to make decisions about which spices to use and how much to include as to not overpower the book completely. An editor can only do so much if the bulk of the story is not already in place.
