Sigmund Freud is the most famous developer of this therapy approach. The therapy concentrates on bringing forward repressed unconscious thoughts. Freud believed that the ego and superego spent a considerable amount of energy to keep these feelings and thoughts repressed. It was this repression and the development of defence mechanisms that left these hidden conflicts unresolved. Freud thought that these unresolved conflicts prevented normal psychosexual development, which in turn caused personality disorders. One of his most common techniques to bring these thoughts to consciousness was the use of free association.