I've got a theory...
I have a theory about Angsty Mary Sue and why she tortures us so. (And why her authors are often insistent she isn't a Mary Sue at all, although I don't have anything even vaguely approaching incidence statistics on that.)
Novice authors are often advised that for a character to be a good, rounded individual, the character must have flaws. In the case of many Mary Sues, this runs smack into the Princess Perfect syndrome. Accordingly, the author decides she has to be imperfect, and gives her a flaw - only one, because in every other respect she's perfect, of course.
However, one single flaw, exaggerated and hammered upon, and usually angsted extensively about, looks bad, because it's unrealistic; few people have one MASSIVE, ALL-CONSUMING personal flaw, because something *that* big tends to get corrected (or at least reduced) as part of the process of growing up. Most people have more subtle flaws, but Mary's author doesn't tend to know how to write a character who's not overwhelmingly perfect without hammering on a flaw like that.
IMO, the art of rounded characterisation lies less in specific flaw but more in credibility in virtues, and an author's willingness to allow the character to make an honest mistake from time to time - without dwelling excessively.
But Angsty Mary Sue seems to come from an honest conviction that this is what Good Characterisation is.
Novice authors are often advised that for a character to be a good, rounded individual, the character must have flaws. In the case of many Mary Sues, this runs smack into the Princess Perfect syndrome. Accordingly, the author decides she has to be imperfect, and gives her a flaw - only one, because in every other respect she's perfect, of course.
However, one single flaw, exaggerated and hammered upon, and usually angsted extensively about, looks bad, because it's unrealistic; few people have one MASSIVE, ALL-CONSUMING personal flaw, because something *that* big tends to get corrected (or at least reduced) as part of the process of growing up. Most people have more subtle flaws, but Mary's author doesn't tend to know how to write a character who's not overwhelmingly perfect without hammering on a flaw like that.
IMO, the art of rounded characterisation lies less in specific flaw but more in credibility in virtues, and an author's willingness to allow the character to make an honest mistake from time to time - without dwelling excessively.
But Angsty Mary Sue seems to come from an honest conviction that this is what Good Characterisation is.