Why did Freud consider narcissism after puberty to be a disorder?

According to Sigmund Freud, narcissism is considered a normal and necessary stage of child development during infancy, when a child is learning to distinguish between the self and external objects.12

However, Freud viewed narcissism as a disorder when it persists after puberty. This is because, in his psychoanalytic framework, healthy development requires the redirection of libido—or sexual energy—outward toward external love objects. When an individual fails to make this transition and instead remains fixated on the self, it represents a developmental arrest or a regression. In this state, the individual's capacity to form mature, reciprocal relationships is impaired, as their psychological energy remains trapped within the ego rather than being invested in others.123