Murphy's Law of Hair

Why is it that your hair never looks as good as it does the day you are scheduled to have it cut?

I just looked in the mirror and thought "I look gooood" (thanks to Roonil Wazlib for that one), and then remembered that I have a hair appointment after work.

Inevitably, if I were to reschedule said appointment, my crowning glory would somehow manage to go from "gooood" to "Good God! Get a brush!" in less than 60 seconds.