Few realizes this, but narcissists think themselves to be a group of one.

This makes their defect more apparent as there is no such thing. Normal groups are large, they seek to accrue more resources, they are never at fault. To point out something for which they'd be at fault for (it can't be true because I would have noticed it) is impossible, possibly because it mean the group would have to split.

How do groups get convinced? The Nazis got convinced when guns were shoved in their faces. No doubt just one year before the end of WWII, they would neither believe defeat could occur or that the Holocaust was ongoing.

It does reveal a toothlessness when facing any sizeable group that is completely incorrect.