I can read a long action packed chapter, but if it is a conversation chapter...even if I like what is being said...I lose interest after about 2000 words. I think in professional novels it is not so bad because you put a bookmark in and set the book down when you get bored. You see the book later and you start where you left off (this is why I have been reading Luke Skywalker and the Shadows of Mindor for three months). In fanfiction you have a tendency to forget what you were reading if the fic gets off of page one. Or if you do see it you can't remember exactly where you left off in that 10K word chapter.