The idea hit me when I was walking home from work one day. It was raining and all I could think about was how a smart move was to bring the umbrella with me at work, even though it was a sunny morning.
Draw a line in the door, horizontally from the door handle. Explain to everyone that everything above the line is Good, Better, Best. And everything under it is Not good, Worse, The Worst. Now you have set up your "Happiness door".