True self-insertion is a literal and generally undisguised representation of the author; most characters described as ``Mary Sues'' are not, though they are often called ``proxies'' for the author. The negative connotation comes from this ``wish-fulfillment'' implication: the ``Mary Sue'' is judged as a poorly developed character, too perfect and lacking in realism to be interesting. In chapter four of her book Enterprising Women, Camille Bacon-Smith states that fear of creating a ``Mary Sue'' may be restricting and even silencing to some writers.
Mary Sue
Camille Bacon-Smith