Very little in a day is under your control, and your attitude is one of the few things that is. John Jacobs of Life is Good suggests swapping the words have to for get to every time you catch yourself using them. Rainy days at camp are the test case. Everything is wet, the best activities are closed, the campers are cranky, and you still get to spend the day at camp.
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.