The first American to construct a comprehensive theory of personality is Harry Stack Sullivan, consisting of the belief the development of personality is from a social context. Sullivan contends without other people personality to not exist. The isolation of a personality from a complex of interpersonal relations can never occur in which the person has his being and lives, according to Sullivan. The knowledge of human personality according to Sullivan can only be gained through rigorous, scientific study of interpersonal relations. The emphasis of his interpersonal theory is on the importance of the developmental stages: infancy, childhood, the juvenile era, preadolescence, early adolescence, late adolescence, and adulthood. A person's ability to establish intimacy with others may determine healthy human development, yet unfortunately anxiety can cause interference with the satisfaction of interpersonal relations during any of the mentioned developmental stages. It may be for preadolescence to represent the most crucial of developmental stages, where children first become capable of the capacity for intimacy yet have not attained an age where lustful interests complicate their intimate relationships. The belief of Sullivan is the achievement of healthy development in people when they are capable of experiencing both lust and intimacy toward the same other person.