planning for the unexpected

At the retreat last weekend, one of the writers asked how you plan for all the unexpected things that come up while you are trying to do what you had planned to do for a given time period. She meant that there are always unexpected revisions that you have to do, and that when you are going to do a school visit or a tour, the day before you're supposed to leave, you find out a list of things that someone else was supposed to do that they didn't, or you are trying to do a collaboration and it tur