Narcissistic personality disorder (NPD) is characterised by a lack of empathy, an inflated sense of self-importance and an intense need for admiration.
Wikipedia

Well, that answers your question: a narcissist is unaware that they are acting in a manipulative and self-centred manner, or how they are doing so. They are thoroughly convinced of their entitlement and the behaviour that stems from it.

However, I see a much bigger problem these days in the misattribution of this personality disorder: it feels as though everyone has several narcissists in their circle of acquaintances and has had to suffer at their hands. Anyone who deviates in any way from normative values is labelled a narcissist. Yet the majority, excuse me, are simply just arseholes...