Understanding Mary Sue Characters

A Mary Sue character is when an author inserts themselves into the book as a character, usually blatantly not necessarily by name. It's considered an insult when someone points out a Mary Sue character in a work, suggesting that the author is fulfilling their wishes through this character by making them all-powerful and omnipotent. To avoid this, authors should create characters with different viewpoints and attributes to prevent them from all sounding the same or resembling the author.