One other important thing I left out above, that might help cast some further light: that self-identifying label of "nice person" (or however else the person wants to be seen: special, badass, smart, lovable, important, whatever) is almost always a defense against deeply felt insecurity. So, Alice, Bob, and Charlie all have deep-down worries that they may or may not be wholly aware of that there is something wrong with them/they're not likable/admirable/something, and the way each of them copes with this is by telling him/herself "but I'm a nice person!" and then seeking out other folks to validate that judgment. The trouble is, as long as there's a mismatch of this deeply-felt unworthiness and the label that other folks are validating, the person seeking the reassurance won't really buy it in the long run, it'll be a temporary fix ("wow, Alice, you're so nice!" "Gosh, thanks" [temporary feeling of security, then, to herself:] "wow, that guy thought I was nice just for that? He was just being polite, he didn't really mean it.")