You know, when thinking up a plot... it's much easier if you just dump a Mary Sue somewhere there (even if just in the backstory). The real world is way too chaotic; so if you want to mimic it, the story needs to be chaotic too. Mary Sues on the other hand provide convolving points for the numerous plot arcs, thus creating a guideline system over the sea of chaos.
Whuh. I just described the theory behind the ta'veren.