I am recycling a cogent post made to John Scalzi's Whatever forum from a couple of years ago because the argument is worth repeating:
http://whatever.scalzi.com/2009/01/28/reasonably-unscrewed-up-character-≠-mary-sue/ Mary Sue/Marty Stu… where to begin?
Probably, I think, with damning this too-timely Scalzi entry coinciding with my current project which includes a character named Martin Stuart.
Yes, John, I agree yet I think you and many of the other posters skimmed a crucial element, which I’ll approach via a reply to one post:
Eddie @71 - what was RAH supposed to do when he was the smartest kid in his school, who “thought in the 5th dimension, bypassing the 4th” [NB: yearbook quote approximate from memory]; was the only successful US Military Academy appointee by his Congressional rep; who stood 8th in that highly competitive class; who was an intercollegiate saber champion; who was an interservice pistol champion; who was the most successful SF writer of the 20th Century; who had friends and colleague like Isaac Asimov, Lyon Sprague DeCamp, Arthur C. Clarke, Fleet Admiral Ernest King, Rear Admiral Caleb Laning, et alia?
RAH liked to write about competent people, similar to himself and those he knew. Robert Sheckley and Donald Westlake frequently prefer to write about amiable bumblers. I highly enjoy the works of all three.
Here’s the crucial elements slighted in the above discussion: is the character, however competent, tasked in the story proportionally to his or her capabilities?
Steve H @62 and Mac @66 partially imply this MS Disorder’s predilection at the expense of story.
What if I were to write a story about a country boy who rode motorcycles standing on his head, regularly blew himself up with dynamite, and allowed himself to be dragged behind race cars for a living [while lighting himself on fire to beat the tedium]; a guy friendly with Clark Gable, Walter Brennan, Bud Abbot & Lou Costello, John Carradine, and Elizabeth Taylor?
Or if I had a character born to immigrant parents within a year of the Great Depression, become a champion varsity 5-letterman in high school and work three jobs [two full-time, one part-time] while completing correspondence school in electrical engineering while he was courting his childhood sweetheart; a guy who would calmly wrestle the short cables in a commercial 240-volt panel with his bare hands as fireworks exploded around him and everyone else headed for the exits or sought cover; a fellow who, as a young minister in the South, successfully opposed the Klan, under threat of violence?
Improbable Mary Sues?
Or my very real paternal grandfather and great-uncle.
In an age of celebrated mediocrity, it’s easy within this fashionable selection fallacy to dismiss everyday competence and the existence of outstanding merit. The military personnel in the responses above remind us of that verity: in this world, there are giants as well as pygmies.
The valid accusation of Mary-Sueism applies to would-be writers who mistakenly outfit themselves as the sole giants in Munchkinville.
The misdirected criticism of Mary-Sueism that John identifies is oft wielded by those hornswoggled into the false belief that giants don’t walk among us.
JJB