Having looked at how surprise might be used in storytelling and the approaches writers can take to creating the unexpected, let's take a look at it from the reader's point of view.
Most readers don't want to be confused, but they don't want to be bored either. Familiar details and predictable sequences can build verisimilitude and help readers to orient themselves and feel at home in a story, but they are always hoping something strange will happen. And, once they've observed a pattern and been engaged enough to use it to predict what will happen next, they hope the writer will change things up.
The way the reader participates in surprise is through anticipation. Working out puzzles, looking for answers, and wanting to know what happens next require an investment on the part of the reader.
That depends upon five things:
First the reader must be engaged in the story. Titles, hooks, and genre tropes can all be used to draw a reader in.
Second, they need to be presented with what is normal. H.G. Wells said, “As soon as the magic trick has been done the whole business of the fantasy writer is to keep everything else human and real. Touches of prosaic detail are imperative and a rigorous adherence to the hypothesis. Any extra fantasy outside the cardinal assumption immediately gives a touch of irresponsible silliness to the invention.” I think this has relevance to all types of fiction. If there are no limits and oddity and change are constant, nothing is unexpected.
Third, the reader must be kept immersed in the story. Language, empathetic characters, and questions all keep them involved and participating.
Fourth is trust. Readers will only invest enough to speculate on answers if they have confidence in the writer. They must believe that the writer is competence and will not cheat them with, say, a deus ex machina.
Fifth, based on the set up, something should be missing. The reader should feel an urge to complete an idea or formulate theories about how questions might be answered. And these can't be just any questions. They must be questions where readers believe the answers will matter, either because they will reveal something or because they will be entertaining or both.
Putting in apparent answers in fine. As much as fairness is a part of anticipation, readers usually want to be misled. Red herrings and distractions that misdirect without being ham-handed are welcome.
One more thing to keep in mind: Engagement requires that the reader will not be repelled by the qualities or the content of the work (although it is possible to push the envelope for readers occasionally). For instance, some people will never watch black-and-white movies. Others have this or reactions against fiction, such as fantasy, that is not mimetic. This is fine. No writer can appeal to everyone. But knowing the audience has these limits and requirements can be a useful guide for a writer.
When answers are delivered, they must be satisfying. They must feel worthy of the investments the readers have made and they must be fair. That is, the answers must be better than what the reader hope for while staying within the boundaries of the information (clues) that have been presented.
So, consider this when you're writing: a surprise only works if readers are actively involved, gathering information, forming their own hypotheses, connecting logic chains, worrying about the fates of characters, and hoping for insights on matters of concern.