Should fiction be believable?

I had the pleasure of watching the movie Prometheus Saturday. I love movies, novels, paintings, songs that challenge my beliefs or make me reconsider my opinions. I love any form of art that pushes the boundaries of thinking and conventional wisdom.

Leaving the theatre it struck me how differently an audience will consider a movie or novel when offering an opinion. Fans of science fiction, for example, accept that a subject in itself is fiction but they are very opinionated if the story does not follow scientific norms.  If a character has the ability to fly there has to be a reason the character has the power to do so. If characters are on an alien planet there has to be an explanation for having a breathable atmosphere. For fans of supernatural or paranormal fiction, there are characteristics of the types of monsters, ghosts, zombies that are accepted and if the writer attempts to stretch or alter those characteristics the change has to be explained or at least understandable to the discernable reader. One can't just sit down and write a zombie story that doesn't follow the nature of zombies unless the characteristical changes are at minimum defined. For the "zombies" of The Raised the search for the truth is part of the story therefore allowing me to bring my readers along for the ride as the mystery is unraveled. 

I could describe every genre of fiction and we would accept there are parameters in each, a Bible if you will, that we as writers abide by.  For me as a writer of dark fiction I have made my first goal that my fiction be "believable" though in dwelling on the subject I wonder myself how I made the decision. Fiction is like freedom, boundless and expanding, and I should not restrict myself to what is "believable" if I wish to tell a story that could be conceived beyond the believable. As a writer I want my fiction to be believable even though I love that my readers have established their own opinions of my work and I would never want to influence their opinions especially if their interpretation of my work makes them love it.

But perhaps the word believable is not the correct word to use. Perhaps it is a requirement that the story simply makes sense, that the reader moves from beginning to end and appreciates the journey? So in asking the question "should fiction be believable?" I need to simply tell myself that fiction only has to be enjoyable. In the constructs of fiction, all things are believable.