You cannot rehearse twelve campers arguing about bedtime, but you can run the whole scene in your head before it happens. The brain fires the same pathways whether the situation is real or imagined, which is why athletes picture a serve before every point. Five seconds of this is a genuinely good trade. It works just as well for a job interview or a test you are dreading.
This is the short version. The full lesson, with the story behind it, is in the book.
Take The Summer Camp MBA with you, or get the field notes by email while you work through the lessons here.