The answer is: Personalities are influenced by unconscious conflicts and desires.
Amongst some of Freud´s most illuminating theories, his conception of desire is one of his most important contributions to psychoanalysis. The idea behind this theory is that the mind is pulled by unconscious and conscious conflicts generated in a life´s time, childhood being most important, and these conflicts are materialized in objects that are deemed valuable (to the acquisition of pleasure) according to the nature of the conflict: how it is represented in the mind according to the pull of the Id, the Ego and the Superego (the tripartite constitution of the mind).