Ask most people why they are happy and the answer arrives in one word: fine, good, no reason. The counting almost never happens out loud.
Done properly it gets specific fast. The dog. A job that is not perfect but is not cruel. The friend who replies at midnight. Bread. A knee that works.
Specificity is the trick. A general sense of things being all right evaporates on contact; the tomatoes on the balcony finally doing something stays put.
Nobody is going to ask you today. Answer anyway, on the walk to wherever you are going.