" We have been able to explain some of them, such as the fear of being alone or in the dark or with strangers, as reactions to the danger of losing the object. Others, like the fear of small animals, thunderstorms, etc., might perhaps be accounted for as vestigial traces of the congenital preparedness to meet real dangers which is so strongly developed in other animals. In man, only that part of this archaic heritage is appropriate which has reference to the loss of the object. If childhood phobias become fixated and grow stronger and persist into later years, analysis shows that their content has become associated with instinctual demands and has come to stand for internal dangers as well. "

― Sigmund Freud , Inhibitions, Symptoms and Anxiety