On page 193 of the classroom companion, under Erikson's psychosocial stages, it states that fixation can occur if someone does not move on to the next stage. Meanwhile, in the after-class practice set #3, the explanation for the correct answer to question 25 says that fixation is only a concept of the Psychoanalytic theory. Which information should I base my studying on? Is fixation a concept of both theories, or just of the Psychoanalytic theory?