
To me, writing fan fic is like playing a video game, whereas writing original fic is like programming the video game.
In fan fic my world is already created, my characters defined; the words, the politics, the settings, the tools, it's all already there for me to use, or abuse, as I see fit. In developing an original story, none of that is there until I create it, until I define it. The slate, she is completely blank. Quite frankly, I find original fic a terrifying process in some ways, liberating in others. At this very moment, however, it's mostly terrifying.
Money quote: "Many of the characters that fall do so not because they are inherently bad or evil, but because the line between acceptable and unacceptable means becomes blurred."
She also points out that we are often easier on characters who behave worse than the hero because we don’t expect as much from them as we do from the hero.