At his inimitable blog, author John C. Wright has an interesting blog post (which is mostly a quote of one of his readers’ comments) about what makes a Mary Sue. The key insight is that the defining characteristic of a Mary Sue is not that she is super-awesome. It’s that she’s super-awesome but we’re supposed to treat her as a young, innocent ingenue:
Rey is great at everything she does. The reasoning behind that may be justified…but that is not the issue.
The issue is that Abrams clearly expects us to think of her as a sort of female Luke Skywalker. Except Luke was nothing like that! We are asked to accept that she is a natural born pilot, better mechanic than Han Solo, better natural Jedi than Luke was at the same point of his training, and a natural swordsman…but we’re ALSO supposed to think of her as a plucky orphan farmgirl.
I think that’s right. A 35 year old queen who is beautiful, intelligent, a skilled warrior and a crafty statesman wouldn’t be a Mary Sue if she’s presented as someone with a past who’s used her 35 years to good effect—if she’s someone who’s already been on the hero’s journey and come out of it having learned some lessons. The real problem comes in when she’s all of those things and only 16 years old.
The commentor which Mr. Wright is quoting calls it fundamental dishonesty, and while I think that he’s right, I’d prefer to call it a fundamental contradiction in the character. What really makes Mary a Mary Sue is when she’s got all of the benefits of experience without having any of the experience. I think that it really comes down to sympathy.
Growing up is rough so (sane) human beings have sympathy for people who are still doing it. We are willing to tolerate all sorts of mistakes in those who are young and inexperienced which we will never tolerate in the old and experienced. (This is why it’s so important to not waste one’s youth and to learn how to be competent while people will still be forgiving of your mistakes.) The upshot is that young protagonists are much easier to write—the audience will naturally be sympathetic with them. The author’s mistakes will get much of the forgiveness that the character gets since the author’s mistakes often are also the characters’ mistakes.
The other thing is that this makes character development a snap. Children don’t know anything and make (nearly) all the mistakes one can make, so giving them something to improve about is trivial. Because of the instinctual forgiveness given to children, they don’t cease to be sympathetic merely because they start out awful, either.
This creates a temptation on the part of the author to make his character younger than he should be because it’s easier to write. A competent adult is much harder to make sympathetic, especially if he has a character arc. It’s easy enough to give him a character arc if you make him start off as a bastard who deserves to be shot. (This is the reason why the Loveable Rogue™ is to popular, by the way—just be careful to say that he’s a rogue rather than show it or the sympathy goes away. Show don’t tell does not apply to flaws in characters you want the reader to like!)
What’s really hard is writing a competent adult with a character arc who starts off as a decent human being. The reason this is much harder, of course, is that the writer has to be better than minimally decent. Because one can’t give what one doesn’t have, one can’t fake wisdom. And the character arcs of decent adults are all about growing in wisdom. A child has the (easy from an adult’s perspective) task of becoming a minimally competent adult. A minimally competent adult has the task of becoming a wise old mentor. Children generally succeed; adults often fail. For that reason, nearly anyone can write a coming-of-age story. It takes a real man to write a story about someone who already came of age.
A Mary Sue is the attempt to have it both ways—to write a coming-of-age story about a competent adult.