Why did Kernberg describe narcissists as vulnerable beneath a grandiose exterior?

According to the theory of psychoanalyst Otto Kernberg, narcissism functions as a psychological defense mechanism. Kernberg posited that this behavior originates in childhood as a reaction to parental coldness, neglect, or lack of empathy, which often stems from the parents' own narcissistic traits.1

In response to this early emotional deprivation, the child experiences feelings of rage and becomes emotionally hungry. To cope, the child attempts to take refuge in an idealized aspect of the self that is capable of evoking admiration from others. This defensive strategy ultimately manifests as a grandiose and inflated sense of self. Consequently, while the individual presents a grandiose exterior to the world, they remain internally vulnerable and continue to question their own self-worth.1