Many of these examples are Plot Twists, so beware of spoilers ahead!
And You Thought It Was a Game moments in Literature.
- In the book Abduction by Peg Kehret, the main character, a thirteen-year-old girl trying to save her little brother from a kidnapper, writes a message on the bathroom mirror of a bar with soap to try to get help. However, it just so happens to be mystery night at the bar, so a waitress, thinking that a patron had written the message to throw people off, washes the message off the mirror. When the story goes on the news and she realizes that the message was an actual cry for help, she feels very ashamed.
- Animorphs:
- The Howlers are savage killers. However, their mind has been compared to a dolphin's in playfulness. They only kill because they have no idea that their victims are alive and feel pain and emotions. Seeing an emotional display causes their master to stop using them immediately as they were unwilling to fight.
- On a wake of a major battle the gang runs into a bunch of tourists, who turn out to be inveterate Trekkies and as such are beyond ecstatic to learn that aliens are real, and insist to help the Animorphs to the chagrin of the latter. It dawns on the patriarch that what he's gotten his family into is neither an elaborate LARP session or the real life version of his favorite show when he hears Jake giving orders about "taking the wounded to cover but living the killed where they are", and he hopefully asks if "killed" means "stunned" to which Jake replies that no, in this franchise "killed" means "dead".
- The central premise of Ernest Cline's Armada is that certain video games are actually training sims for an impending alien invasion, with the latest games being near perfect simulations of actual combat against the aliens. And because Earth's defenses are drone-based, certain "game" missions are actual combat operations.
- Bang! You're Dead by Ray Bradbury centers on a US soldier called Johnny Choir fighting in Italy in WWII. He believes the entire war is a game and no one actually gets killed or hurt - they're all just pretending. This allows him to "duck" bullets, because he doesn't think they exist. When another soldier called Melter tells him it's all real, Choir promptly gets shot. The same thing happens to Melter when he tries to do what Choir did to avoid being hit.
- In Dead Man's Folly by Agatha Christie, a famous detective writer has been asked to organise a Murder Hunt as one of the activities in a village fete. She begins to feel that she is being manipulated via proxies into changing details of the fictional murder to fit someone else's script, and calls in Hercule Poirot because she feels a real murder might be on the cards. The girl playing the "dead body" is duly killed for real.
- In the Discworld novel Going Postal, Moist von Lipwig is totally unconcerned about facing down a pack of angry guard dogs because he knows that all purebred Lipwigzers (the Disc's version of Rottweilers) were trained by his countrymen (they don't let females out of the country, to keep the breed price high). He successfully uses his granddad's commands to control them, but later learns they were Ankh-Morpork mongrels that looked like Lipwigzers.
- A Doctor Who Expanded Universe novel introduces a free video game the premise of which is a war between a race of porcupine-like aliens (whom the game labels as the good guys) and a race of mantis-like aliens (the game's bad guys). Since neither race can kill one another in hand-to-hand combat (the porcupines' needles can't pierce the bugs' exoskeleton, and the bugs' claws can't get close to the porcupines' bodies due to the needles), the porcupines recruit humans (players) to infiltrate the enemy base and win the war. A typical first-person shooter, except the save game, for some reason, occasionally gets erased, forcing players to start from the beginning. It turns out that not only is the premise true (except for the porcupines being the good guys), but the aliens are kidnapping humans to use as the in-game "avatars" controlled by players (when players "log out", the avatar just stands there until the player comes back or when the bugs kill him/her). The Doctor is playing the game until he finds out that his avatar is Rose.
- The main character of Dokkoida?!?! agrees to put on the costume and fight supervillains because the costume contains a special component which boosts his fighting ability, all while playing dramatic music... except that the end of the first episode reveals that the suit manufacturer forgot to put that specific component in, leaving only the music. The other characters don't bother to mention this fact to him until the last episode. Suzuo also put on the suit because he didn't take the claims about fighting supervillains seriously, since the suits makers were a toy company. He realizes too late that toy companies can make weapons too.
- In John Dickson Carr's Dr. Gideon Fell novel The Arabian Nights Murder, a set of friends putting on an act to trick one of their buddies hires an actor to play a professor in an Arabian museum. They are surprised when a real professor, a friend of the museum's owner, arrives for a meeting and is treated as an actor who looks just like the real thing. In the meantime, the professor thinks that the actors are real, and attacks one of them in an act of misguided heroics.
- The Eminence in Shadow: Cid Kagenou is a total Chuunibyou and thinks that his friends are just playing along with his roleplaying, unaware that he and his friends are actually fighting real villains.
- The climax of Ender's Game. Ender and the other Battle School graduates are sent to Command School, where they are sent through a grueling set of fleet combat simulations. When Ender realizes that they will never stop trying to skew the odds against him, he decides to sabotage the "test" and prove he's too unstable to ever be put in real command, and pulls a Game-Breaker in the most spectacular way conceivable by ordering a suicide attack against the enemy homeworld, resulting in its destruction and the annihilation of an entire alien species, along with the human fleet that had delivered the death blow. He doesn't take the truth well...
- In volume 13 of Goblin Slayer, the guild arranges a dungeon exploration contest in a practice-dungeon for prospective new adventurers to try out their skills. During Scrawny Girl's run, she winds up getting attacked by a real goblin (rather than the puppets the guild set up) and going down the secret passage it came from. After finally finding her, Goblin Slayer doesn't have the heart to tell her that all the monsters she took down were very real and not just part of the test.
- In Halting State by Charles Stross, the British and Chinese intelligence agencies both run Alternate Reality Games in which player-characters pretend (or rather, think they're pretending) to be spies, essentially creating hundreds of agents who Know Too Little. However, most of the game really is a game, with no "real" opposition or consequences for failure. It's a simple way to sort out potential recruits, provide them with training, and actually make money doing so. It's noted that you can't entrust anything dangerous or time-critical to people who think they're just playing a game in their spare time.
- Harem in the Labyrinth of Another World has the protagonist believe that he's in an extremely immersive VR RPG, even commenting on how crazy the blood splatter effects are when he cuts down bandits. However, once he finishes his first encounter and tries to log off, it dawns upon him that he's actually transported to another world (albeit an RPG Mechanics 'Verse) and that the bandits he killed were real.
- In The Looking Glass War, the rivalry between British intelligence services the Department and the Circus means that the Circus is told that they're just providing support for a training exercise, when it's actually for the Department's first live undercover operation in years, putting an agent into East Germany. Subverted as the Circus is well aware it's a lie, and is waiting for the operation to fail due to the Department's incompetence.
- A nasty example of this trope shows up in Magic: A Fantastic Comedy, by G. K. Chesterton. A certain Conjuror is putting on a show for a Miss Patricia Carleon, her family, and certain of her father's friends. Unfortunately, Miss Carleon's brother suffers from a particularly virulent strain of Scully Syndrome, and upon finding himself unable to explain how the Conjuror managed one particular trick, he collapses in gibbering lunacy. A Doctor who happens to be present explains that the only hope for the lunatic is for the Conjuror to explain how he did his last trick. Then we get this exchange:Conjuror: You would really be willing to pay a [very large sum] to know how I did that trick... But suppose I tell you the secret and you find there's nothing in it?
Doctor: You mean it's really quite simple? Why, that would be the best thing that could possibly happen. A little healthy laughter is the best possible thing for a convalescence.
Conjuror: It is the simplest thing in the world. That is why you shall not laugh.
Doctor: Why, what do you mean? What shall we do?
Conjuror: You will disbelieve it.
Doctor: And why?
Conjuror: Because it is so simple. (Jumps to feet) You ask me how I really did the last trick. I will tell you how I did the last trick. I did it by magic. - The central theme of The Peripheral by William Gibson. In the 22nd century, a method of transmitting information to and from the (or rather, "a") past is discovered. One character who learns of this uses it to set up a system whereby someone from the past remote operates her bodyguard drone. In the mid-21st century, a playtester is baffled by the "VR game" she's testing, and even more so when witnessing an "in-game" murder leads to her being in real danger.
- The Endymion in Dan Simmons' Rise of Endymion does some pretty bad ass acrobatics on a mountain cliff, all the while thinking that dropping would be such a hassle because somebody would have to retrieve him from the safety line. Just until he sees some fearful friend rush to him with just that safety line he forgot to attach. Considering the circumstances, his lapse of mind is easily forgiven, though.
- The biggest issue of the Sword, Spear and Bow Heroes in The Rising of the Shield Hero is the fact that they refuse to acknowledge the world they're in is not like the videogames they're familiar with. This results in them not caring about the consequences of their actions and causing more harm than good along the way, often having the titular Shield Hero having to pick up the slack and clean up their messes.
- In the Star Trek novel The Three Minute Universe, a Glechenite that was taken hostage by Sackers told Kirk that the Sacker ship clearly outclassed the Glechenite ship and shot all around them for sport before finally getting bored and shooting them down. It was later revealed that their command crew had been killed during an accident and the inexperienced crew that stepped up really was having trouble hitting their target.
- In the Star Trek Novel 'Verse book The Captain's Daughter by Peter David, Sulu's Meet Cute with Demora's mother takes place in a theme-park city designed to look like a Wretched Hive. So when Sulu finds himself caught between a band of ruthless criminals and a beautiful freelance adventurer, he naturally assumes this is an act, possibly something Chekov set up because he was complaining he was bored. He keeps thinking this right up until the criminals vaporise someone's head.
- Philip K. Dick's Time Out of Joint. The main character lives in a quaint 1950's town and spends his days solving a newspaper puzzle, "find the green man". It's actually the future, there is a war between Earth and Mars going on, and the protagonist used to be a genius tasked with predicting the Martians' attack targets. After he had mental breakdown, he was given false memories and led to believe that he's living an idyllic life in a fake town. He is still doing his job, by regularly solving what he thinks is just a newspaper puzzle.
- Another dramatic example: in the sci-fi novella Wine of the Dreamers, Raul Kinson is raised in a dwindling alien compound and believes the devices he periodically sleeps in are advanced virtual reality devices that create three alternate worlds within the dreamers' minds. Killing or humiliating dream characters is a popular sport. Unfortunately, the dream worlds are actually long-lost colony planets, one of which is Earth! Over the course of millennia, the dreamers have destroyed space programs and even triggered nuclear wars due to a misremembered plan that the "dreams" must end when the colony worlds achieve interstellar flight.
