When most of us hear this word, we think of someone who thinks about themselves all the time, who never considers others, who always wants to be the focus of attention. This is somewhat true, but it implies choice.
What seems obvious to me now is that such people are made defective very early in their lives by what I suppose we could call Disconnection Trauma. When as infants or toddlers they seek mirroring behavior in their caregivers, it is absent. They share their feelings, and nobody cares, nobody responds appropriately, in an “attuned” fashion. This is horrifying and not processable by someone that age. So instead they seek from themselves the reactions and feedback that was absent in their environment. They learn, at a very early age, and well before formal memory development, that they can trust only in themselves, that they must make a world of themselves, that–this is important–there is no one else out there, or else they would have cared for them, and nurtured them.
So at root it is a muted or absent capacity for emotional connection and intimacy. It is precisely a defect, a gap, evidence of a loss long ago. It is a type of trauma, and should I think best be labeled as such, particularly if we are to develop methods for helping people cope with these sorts of primal losses.