At the dark heart of narcissism is a void.
This central void is fuelled by a lack of identity and sense of self which makes a person suffering from narcissism painfully dependant on others for self-definition, although (as we all know) they would run a million miles from admitting dependance.
A narcissist’s sometimes perplexing behaviour can be explained as an attempt to fill this central void with reflected glory.
Although grandiose narcissists appear socially successful and at least initially confident and friendly, they are still vulnerable to, and dependant on external validation for their self-esteem.
Both forms of narcissism are thought to “share common meta-cognitive deficits which result in conflicting feelings of grandiosity and vulnerability, however they cope by suppressing one and projecting the other, resulting in different presentations (McWilliams, 1994).” [My emphases]