Okay, not in a fight club, battle to the death with Original Star Trek fight music blaring in the background type of way--but still, a fight of sorts.
Writers need to always keep in mind what the reader probably knows from the real world. This can be a problem of focus: don't step by step me on how to start a car unless there is something new or unique about it, or the car is going to blow up, fly, or vanish. Most people know how cars work. When an author focuses on a mundane, everyday thing, I'm waiting for something NON-mundane to happen. When it doesn't, I become peeved. Peeved readers bad.
Another problem with reader knowledge is common and assumed myths. Even though the author has created a world different from ours, they can't shut off what readers know. I just read a book where the main character (who knows vampires) can't figure out why the vamps keep insisting she invite them in. This popped up four times--each time I kept saying in my head, "No, don't go there, author--everyone knows you can't invite a vampire in your home!" I was annoyed that something that is common myth to most readers was going to be a plot point.
And it was.
Now, first off, vampires don't exist--yes, I do know this. But, for folks who read or watch stuff with vampires--having to invite them in is fairly common. So, me as the reader "knew" what an expert in vampires didn't in the book.
Also to be fair, at nowhere in the book had that topic been introduced, and it appears to be limited to a type of vampire. Logically, the author was fine to do what was done. She didn't break her story mythos. But it still bugged the crap out of me as the reader because I knew what was coming.
The author could have found a better way to make the character be in the same pickle, without annoying readers.
Even when you make up your own worlds, you can't shut off reader knowledge.