Like many authors, I have an inordinate fondness for interesting words. One of my favorites is “verisimilitude”, both because its etymology is straightforward—veri = truth plus “similis”=like—and because it is a crucially important concept to put into practice in one’s writing.
Much fiction writing includes inventing a world in which the story takes place—science fiction and fantasy writing for sure, and straight fiction to some extent as well. The characters live in this fictional world, interacting with each other as well as with the world.
Now part of the magic of the process of reading is that the reader will happily follow the writer through the story but only as long as the components seem plausible. Do they possess ‘verisimilitude’? If so, the reader is happy to continue on through the story. If not, the reader will be jolted out of the story as they question what they just read, and look it over again to make sure they didn’t get it wrong. The reader usually has a pretty generous latitude in what they’ll believe. After all, they want to believe the overall story. If the offense is too great, however, they will only grumpily proceed, annoyed that this or that piece of the story seems wrong.
Your story’s world seems to be fairly similar to ours, but somewhere in Chapter 2, with no prior warning, your main character kills a dragon with a magic sword. If you hadn’t dropped in subtly somewhere previously that magic swords exist (let alone dragons!) in your world, your reader is going to be very confused, and not a little irked because they’re going to stop reading and flip through Chapter 1 seeing if they’ve missed something important. Not an optimal reading experience.
However, if you had shown early on that your main character lived in a castle and her mother was training her in witchcraft by casually including a scene where she is reading through a book of spells and waving her wand around, the sudden appearance of the dragon in the next chapter wouldn’t be so startling. A little foreshadowing goes a long way.
There are some examples that seem to contradict this: Gregor Samsa finds himself metamorphosed into a giant insect in the very first sentence of Kafka’s famous short story. The events that occur afterwards are completely believable, however, and serve to buffer the unexpected initial event.
Even very small inconsistent details can jerk readers out of their reverie if they’re noticed. For example, if in your novel’s world Britain and the US never quite make up after the Revolutionary War (as they don’t in my Airship Flamel Adventures series), it would seem unlikely that Americans drink tea out of Wedgwood porcelain teacups.
Similarly, in describing futuristic technology, it’s not important that your airship operate using actual true-to-life technology. But it is important to allow your reader to believe in your technology by sprinkling around a sufficient amount of reasonable-sounding details. No one who watches Star Trek doubts the ability of the warp drive to propel the Enterprise to trans-light speeds after hearing about nacelles, Jeffries tubes, and plasma conduits. (I am reserving my position on mushroom-powered drives, however.)
As a writer, your job is to create entertaining and interesting stories, and that means leading your reader along by the hand through your carefully constructed world, free of jarring inconsistencies and implausible events. Verisimilitude is the answer.