This paper focuses on the concept of “development” presenting behaviour as the result of a complex interaction between nature and nurture, between genetic vulnerability and early object relations. The author underlines that at the end of development the individual has developed the capacity to contemplate him/herself and others in psychological terms and she/he has constructed an internal working model on the basis of which they are capable of organizing their environment and anticipating what will happen in the future, functioning autonomously and no longer being dependent on the presence of others.