A few observations about horror after reading too much of it:
The best horror tropes don't announce themselves. A haunted house is a trope. A possession story is a trope. The "we shouldn't have moved here" setup is a trope. But when a writer nails the emotional logic underneath, the trope becomes invisible. You stop noticing the scaffolding and start checking the locks on your doors.
Paul Tremblay's A Head Full of Ghosts is built on a question it refuses to answer: is the teenage girl actually possessed, or is she severely ill while her family falls apart around a reality TV crew? The whole novel runs on that ambiguity. Tremblay teaches math during the day and coached Little League for years, which I think about more than I should. There's something about a person who spends his afternoons keeping score at a kids' baseball game and his mornings writing fiction designed to make you distrust your own perception.
Horror tropes wear out fastest when the writer uses them as shortcuts. "The lights flickered" is a trope. So is "she felt a chill." So is the thing in the mirror that's there for one frame and then gone. These aren't bad on their own. They're bad when the writer drops them in and moves on, expecting the trope to do the scaring. The trope is just a container. The fear has to come from somewhere specific.
Tananarive Due once said, "Horror is one of the very best genres for social commentary because it literalizes our worst fears." Her fiction proves this repeatedly. The Good House takes a family's generational trauma and gives it a physical address, a house in a small Florida town where something terrible happened decades ago and never really stopped happening. Due's horror doesn't invent its darkness. It finds the darkness that's already there in the historical record and gives it teeth.
The "don't go in there" problem is real, and most horror writers solve it wrong. Characters who walk into obvious danger for no reason break the spell. Characters who walk into danger because they have a reason that makes sense to them, because the kid is still inside, because they don't believe the threat is real, because leaving means admitting something they can't face, those characters pull you in with them.
I've started to think that horror and tragedy are closer than either genre would like to admit. Both depend on a sense of inevitability. Both ask the reader to watch something go wrong that can't be stopped. The difference might just be speed. Tragedy takes its time. Horror tends to sprint.
The scariest moment in most horror novels isn't the reveal. It's the paragraph right before the reveal, when the character knows something is wrong but hasn't turned around yet. That gap between suspicion and confirmation is where dread actually lives. Once you see the monster, you can start problem-solving. Before you see it, you can only wait.
Ambiguity is harder to write than certainty. Tremblay's The Cabin at the End of the World forces a family to decide whether four strangers at their door are delusional or telling the truth about the apocalypse. The novel ends without confirming either reading. That takes more craft discipline than a clean resolution, because the writer has to build a story that works in both directions simultaneously.