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The key question is: Why should I care? Part of the reason people like a book is because they get invested in the plot and the characters. They continue reading because they have a vested interest...
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Source: https://writers.stackexchange.com/a/36680 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
The key question is: **Why should I care?** Part of the reason people like a book is because they get invested in the plot and the characters. They continue reading because they have a vested interest in seeing things play out. They care about what the characters do, what happens to them, how goals are achieved, how the antagonist is foiled, etc. A potential issue with (bad) "dark" books is that there's never anything to get invested in. The characters are shit, their lives are shit, everything they try turns to shit in a rather predictable way. There's no reason to read on because there's nothing to get invested in. _Dark books aren't the only ones who suffer from this._ "Happy" books can fall into a similar trap: the protagonist are perfect paragons, their lives are perfect, everything they do turns out perfect in a very predictable way. Readers don't get invested in those books either. The only difference is that writers are aware of that trap, and there's plenty of writing advice to make sure you have "conflict" in the story. Dark books, though, suffer from a misperception that "conflict" means "bad things happen to the protagonists", such that people mistakenly think a dark book has conflict by the very nature of being dark. That isn't the case: "conflict" goes both ways. Yes, there isn't any conflict if the protagonist simply waltzes through the story, but there also isn't any conflict if the antagonists (be they animate or inanimate) just waltz through the story. If the protagonists never productively engage the antagonists (even in an inevitably futile sense), you don't have any conflict and you don't have a story. Readers can get invested in a dark and tragic book, but they need some reason to care what happens. There needs to be productive conflict, even if the protagonists are fated to fail. There needs to be some reason to care about what happens to the main characters and their struggle - not like, necessarily, but care. There needs to be some mystery in how things turn out. Not necessarily _if_ the protagonists will succeed or fail (there's a slew of books where the heros' eventual winning is never in doubt), but more of _how_ they're going to succeed/fail. All of that is achievable with a "dark and tragic" book (as pointed out in examples in other answers). A final note - you will inevitably get some subset of your readers who won't like your book because of the dark tone, or the fact the protagonists almost never win, or that it's lacking any "likable" characters, etc. That's okay. Not every book has to appeal to every reader.