The focus of psychodynamic psychotherapy is understanding how past experiences influence present behaviours. Psychodynamic psychotherapy can be divided into two subtypes: brief or time-limited therapy and long-term or open-ended therapy. The core concepts of psychodynamic psychotherapy include the unconscious, transference, counter transference, resistance, multiple functions, authenticity and a developmental perspective. Long-term psychodynamic psychotherapy is derived from psychoanalysis and the work of Sigmund Freud. Freud's original focus was on the topographic model, which involved a three-level hierarchy of conscious, preconscious and unconscious domains. The technique of dynamic therapy has evolved from a largely silent and nondirective role for the therapist to one in which the therapist is lively and interactive. Dynamic therapy often requires a considerable length of time because many patients will tenaciously hold on to self-defeating patterns and problematic object relationships. Patients must repeat the old patterns again and again to understand them in different contexts.