In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Butterfly
If you dream of a butterfly then you will enjoy happy times. If the butterfly sits on you then, at the present moment, there is a person who is distant from you but who thinks of you a lot.