Development is a continuous process, each stage being contingent on and influenced by the previous one. In the ordinary course of maturation, if things are to go well, the infant will establish within himself secure figures who will be a source of strength for his developing ego and who will provide inner containment for powerful feelings and anxieties that threaten to overwhelm him. Melanie Klein showed in her work with children that this process begins in the early days of life and that the establishment of this internal world comes about through complex interactions of projection and introjection. In her paper The mutual influence in the development of the ego and the id (Klein, 1952/1980b) she wrote:

By projection, by turning outward libido and aggression, the infant’s first object relation comes about . . . and owing to a process of introjection this first object is taken into the self.