Adult children have difficulty with intimate relationships. Adult children over-react to changes over which they have no control. Adult children constantly seek approval and affirmation. Adult children feel that they are different from other people. Adult children are either super responsible or super irresponsible.
Adult children are extremely loyal, even in the face of evidence that the loyalty is undeserved.
Adult children are impulsive. Adult children guess at what normal is. There is no frame of reference for what it is like to be in a normal household. You also have no frame of reference for what is O.K. to say and feel. In a more typical situation, one does not have to walk on eggs all the time.