A unicorn in the garden is only allowed in chapter one. If something like that appears, without warning, in chapter 17 the readers are likely to rebel, even if it was foreshadowed. Those who want unicorns will have been put off by the 16 unicornless chapters, while those who dislike them will be annoyed by their sudden appearance, and they will probably not be familiar enough with unicorn conventions to have recognsied the foreshadowing.
More generally, any sudden shift in genre or tone can throw the readers. E.g one author wrote a decent story about family relationships stressed by an SF plot device, then decided to expand it into a trilogy. A few chapters in the sequel, it turned into a space opera, with moons being vaporised. Reader reaction was so bad, the writer abandoned the trilogy.
Rapid power escalation has the same problem. If the protagonist is a demigod from page one, or if they find an artifact of ultimate power on page three, the reader can accept that. If they go from Mr Average to godlike over 30 chapters, that's a major change in the scale of the action, and there are problems keeping the story balanced throughout.
In the first chapter of a new story, you've got free license to be as radical as you like, so long as you don't loose touch with the base story, but that's a one time chance. Use it or loose it. After that first chapter, twists have to be heralded, and taken slowly, or the readers will be lost.
More generally, any sudden shift in genre or tone can throw the readers. E.g one author wrote a decent story about family relationships stressed by an SF plot device, then decided to expand it into a trilogy. A few chapters in the sequel, it turned into a space opera, with moons being vaporised. Reader reaction was so bad, the writer abandoned the trilogy.
Rapid power escalation has the same problem. If the protagonist is a demigod from page one, or if they find an artifact of ultimate power on page three, the reader can accept that. If they go from Mr Average to godlike over 30 chapters, that's a major change in the scale of the action, and there are problems keeping the story balanced throughout.
In the first chapter of a new story, you've got free license to be as radical as you like, so long as you don't loose touch with the base story, but that's a one time chance. Use it or loose it. After that first chapter, twists have to be heralded, and taken slowly, or the readers will be lost.