Uttered by the main character/Narrator to the audience, to indicate that a major plot is about to happen.
This line probably originated in 19th Century English romance/gothic novels. The heroine innocently takes a "position" or visits some place where evil lurks or adventure looms behind a calm, civilized veneer. She begins the narrative of the novel, with classic British understatement, something like this: "If I had but known that I would soon be facing a madman with an axe in those dank catacombs, I would never have had the courage to get on the train to Sussex that fatal day last summer . . ."
Related to How We Got Here if it gives away unlikely-sounding details of the plot ahead of time. Found only in first-person narration and omniscient narration with a chatty narrator. Since it's basically a way to invoke Foreshadowing without any actual, you know, foreshadowing, it's a Discredited Trope.
- Peanuts: Lucy tells Snoopy he should start one of his novels with "unbeknownst to everyone" instead of his usual "it was a dark and stormy night". "Unbeknownst to everyone, it was a dark and stormy night".
- Aska: During Motor-Oil conversation with his ex's answering machine, he starts telling a story and eays this phrase after introducing the characters.
Motor-Oil: Little did they know the horror that awaited them!
- The Great Mouse Detective: Dawson's last line of narration is "Little did I know that my life was about to change forever." From there, he meets Olivia and the plot proper kicks off.
- Return of the Jedi: The phrase appears in the Opening Scroll regarding Luke not knowing about the construction of the second Death Star. As it turns out, this would lead him to the final battle against the Emperor and Darth Vader.
- Stranger Than Fiction: Conversed seeing that it's in many ways a movie about stories and tropes, it features a literature professor who explains that he's taught "entire seminars on 'little did he know.'" It's also a subversion —the main character can hear the voice of the narrator, and so knows very well what he should little know (specifically that he is going to die soon), and spends most of the film trying to prevent it.
- Angels & Demons: When Robert Langdon hears in passing a factoid about how a reasonably small piece of cloth can significantly reduce an object's falling speed, he remarks (in narration) that he didn't then realize this information would later save his life. The payoff doesn't come until near the end of the book when the reader has probably forgotten it.
- Ciaphas Cain: Every book starts with a variation and Cain repeats it regularly. He also comments that he'd be "gibbering in terror" if he only knew... It's greatly toned down in the 4th and 5th books and worded a lot better.
- "Don't Guess, Let Me Tell You": Satarized as "The HIBK (Had I But Known) School" in this Ogden Nash poem which goes on to give numerous over-the-top examples:
Sometimes it is the Had I But Known what grim secret lurked behind that smiling exterior I would never have set foot within the door,
Sometimes the Had I But Known then what I know now I could have saved at least three lives by revealing to the Inspector the conversation I heard through that fortuitous hole in the floor.
- The Goon Show has used this for comedic effect.
Seagoon: (after two other characters have made asides to the audience) Little do they know how little I know about the little that they know. If only I knew the little they know about the little that I know, then I'd know a little. I'll have to keep my little ears open, you know.
- Lux Radio Theatre: In their adaptation of Pinocchio, Jiminy Cricket uses the phrase during a transition between scenes.
Jiminy: (narrating) Yessir, there we were, free as the air and on our way back to Mister Geppetto's. But little did we know, little did we know, that even then, new deviltry was hatching. Down in a waterfront dive known as the Red Lobster Inn, Honest John, and his crony Gideon sat drinking beer. With them was a companion, an evil-faced, leering Coachman...
- Aquaria: The early stages of the game are narrated by Naija expressing just how ignorant of the world around her she was at the time.
- Darkwing Duck: One episode that takes place in Medieval times parodies this. Darkwing's public persona is working in the royal castle. After watching the King and Queen acting like fools, he turns to the camera and says, "Little do they know... And I do mean little."
- Duck Dodgers in the 24½th Century: Dodgers (Daffy Duck) is accosted by Marvin the Martian, brandishing a disintegration gun.
Dodgers: (to camera) Little does he realize I have on my disintegration-proof vest. (to Marvin) You may fire when ready, Grisly. (he does; Dodgers is disintegrated; the undamaged vest hangs in midair for a moment then plops into the pile of ashes)
- Ed, Edd n Eddy: Ed begins his portion of the "Rashomon"-Style story in the episode "Once Upon an Ed".
Ed: And so it went! Little did Ed, Edd, and Eddy know that...