It's kind of like seeing a Necker cube shift, or one of several other optical illusions that can appear as one thing, until you see the other. But we are blind to what we don't know. Once you see it though as false confidence, from that point on the changes in perception begin to take hold and grow.
Indeed, there is absolutely nothing anyone can say that will change someone's mind who has fallen under the spell of charming, love bombing, mirroring, over-the-top confidence, etc., until they see it another way for themselves. The best anyone can do is warn, then step back and wait it out for them to make that mental shift. It's unfortunate for a couple of reasons -
Often someone who fell for the show/act of confidence ends up feeling badly hurt, but it's also unfortunate for those with a PD. They are mostly reacting to what they are rewarded for, and as long as there are others who encourage them to remain as-is (and there always be), there isn't much motive to change. They are stuck too in their perceptions because '...but others approve of me, you don't anymore, so the problem must be you...' They aren't wrong in seeing it that way.
It's why when you meet someone who has an extreme personality like NPD or HPD, the crowd will often be split into those who approve to an extreme, and those who are going WTH!

Extremes tend to result in extremes.