http://mythicscribes.com/world-building/writing-believable-fantasy/ Maintaining your audience’s suspension of disbelief is a challenge that every fantasy writer must face. Obtaining, and holding, that suspension relies on your ability to convey a believable story, setting, and cast. If the suspension of disbelief is dissolved, so is the reader’s will to continue on with the story. So, how do we make fantasy believable? Consistency is what maintains the suspension of disbelief throughout the narrative, and keeps your readers comfortable in your fantasy world. It makes it possible for their minds to accept new developments, so long as they do not drastically break from what has already transpired.... Your audience needs to believe that what’s happening in your fantasy story is consistent with the world that you have presented. Obeying your fantasy universe’s laws and rules ensures that the story is believable. When you do introduce new fantasy elements, a few questions should be asked: Would this new element be better introduced earlier in my narrative? Does this break any of the laws of my fantasy world? If this new element is a departure from the established rules, should I let my audience know ahead of time that this might be possible? If I was a reader, would I want an explanation for this new element? The important thing is that you do not shatter the consistency by breaking the universal rules of your fantasy world.