This works on other occasions also. When negative feelings plague you, push them away by repeating, "Good!" and watch what happens. Or when you want to remember something from the past that is good, but you can't quite think of it, say, "Good" and all sorts of past memories that are good will spring to mind. Hopefully one of them will be the one you want.
But you have to say the word with meaning. There are ways to say good and really mean bad. This only works if you mean what you say!
Make it a good day!