Horror – in any medium – has a weakness. It’s almost always too long. And long horror doesn’t really work – it might start off strong, but it slowly attenuates, ending in anticlimax.

Before I begin justifying that, I should note that I’m going to be using lots of examples from various things. Let this serve as a general warning against spoilers.

Most genres take their name from their content – romance novels are about romances, science fiction involves science, etc. Horror is different – it’s the only genre I can think of that is named for its intended effect. Horror is a genre that attempts to horrify, to scare its audience. Horror is supposed to keep the reader/viewer at a fever-pitch, scared witless throughout.

I should stress at this point the importance of the distinction between action and tension. “Keep the reader at a fever-pitch” does not mean constant jump scares. Pacing is important in any genre, perhaps especially horror – there need to be moments of relative calm to offset moments of frantic action or panic. With that said, a calmer moment does not mean that all tension is released – in good horror films, even when nothing dangerous appears to be happening at all, the tension is still there – the audience doesn’t know it is safe, and is waiting for the threat to appear. The absence of present threat doesn’t stop it being horror – the neutralisation of threat does.

In a novel or full length film, it’s rare that the entire thing is actually horror. The audience ends up only scared for part of the film, generally the first part. The problem is that, with a longer work, there’s too much development. The monster becomes too familiar, or even gets defeated.

Both of those things limit how effective horror can be. If the humans win in the end, then the audience isn’t horrified – they’ve been presented with a solved problem. Yes, the aliens might seem dangerous, but they’re defeated by water. You could have worried that the slasher was right behind you, but you just saw him get shot (repeatedly) in the face, so he probably isn’t. If the trope-blind idiots inhabiting a horror film can deal with whatever ghost they are facing, the audience definitely can.

“But a spider was, after all, only a spider. Perhaps at the end, when the masks of horror were laid aside, there was nothing with which the human mind could not cope.” – Stephen King

Likewise, if the threat becomes too familiar or well-understood, it stops being scary. Fear of the unknown is always more potent than fear of teeth or chainsaws – you can deal with a fisherman wielding a hook, but you can’t even begin to fight back if you don’t know what you are facing. The Village is probably the most obvious example of this; the first appearance of the monster wastes all the tension that has been carefully built up to that point. Once you realise that the beast is an arthritic hedgehog, you can’t be horrified any more. If you know how to escape, hurt, or kill the monster, then you don’t have to worry.

“If it bleeds, we can kill it.” – Predator

It’s very hard for full-length films or novels to avoid those issues. In an hour and a half, the audience is going to learn a lot about the monster. If they didn’t learn anything, then the film would just be occasional screams in the darkness – there needs to be some sense of progression, of building tension. But an hour and a half, or a hundred thousand words, is too long; we learn too much. We learn exactly what it is, and exactly how to kill it – at that point, the monster should be afraid of the characters, not the other way around.

The concept of ludo-narrative dissonance is the idea that a game’s mechanics can clash with its story line; you’re supposed to worry about the invading orc army, but you’ve just fought your way through hundreds off them. You’re able to transform into a giant stone golem, but you have to find a key for the fragile wooden door.

A similar concept applies to horror – the mechanics of horror clash with the mechanics of narratives. Stories – especially novel/feature-length stories – have arcs and character growth and resolutions. Horror doesn’t, and shouldn’t, because all of those things take away the fear.

Stephen King’s It has this issue. The first half I would recommend to everyone – it made me afraid of the dark again. Helpless children are stalked by a lurking, ever-shifting terror. It hunts them, mocks them, toys with them. Pennywise is one of the best-written and most affecting monsters I’ve ever come across.

“They float,’ the thing in the drain crooned in a clotted, chuckling voice. It held George’s arm in its thick and wormy grip, it pulled George toward that terrible darkness where the water rushed and roared and bellowed as it bore its cargo of storm debris toward the sea.” – It, Stephen King

But that’s all ruined by the second half. The second half of It is a bloated mass, undoing all of the creeping horror. The reader learns too much about the monster – it’s not an unknown quantity any more, but a phobo-phagic space monster, and there’s a whole, huge but ultimately understandable, metaphysical dimension. And suddenly, Pennywise isn’t scary any more. In fact, he’s kind of pathetic. He’s not the avatar of fear itself, he’s a squatting ugliness that can be hurt by inhalers.

If the monster becomes vulnerable, shows weakness, becomes too well-understood, then you start to feel sorry for it. Gollum is terrifying when he’s trading riddles and sneaking up on Bilbo in the dark, but he ends up not even worth killing. All the fear flows out at once. Both Pennywise and Gollum end up in the same place – barely worth killing.

Pity? It was pity that stayed Bilbo’s hand. – The Fellowship of the Ring, J. R. R. Tolkien

It’s an issue – the second half of horror works, the bit that should be the climax, is rarely as scary as the first, nominally safest, section. Too much has to be revealed, too much has to be made clear. It’s a narrative requirement that clashes with the intention of the work.

Of course, steps can be taken to mitigate this. Jaws is a masterpiece because it avoids revealing the monster as much as possible. True, this was due to technical difficulties rather than anything else, but it’s still a good example to follow. Because the shark is so rarely seen, it has a big impact when does appear, and the film uses constant misdirection to stop the audience knowing what it will do. The use of music is also worth noting – it accompanies all the shark attacks but the last one, which means the audience can’t predict it, but thinks they can. Jaws keeps the audience confused and insecure, and that’s where fear comes in.

The shark is also never properly vulnerable. Yes, it dies at the end, but this is clearly presented as a last ditch effort, a fluke. Up until that final explosive moment, it’s unstoppable, dealing with everything they can throw at it, even destroying the person most equipped to defeat it. Its death is chance, which means that the audience can’t feel secure; it’s not a truly solved problem.

“Careful. This is the moment when the supposedly dead killer comes back to life, for one last scare.” – Scream

Very few horror stories are as well constructed as Jaws. Some rely on changing location to resolve the story, assuring the reader that there is still a threat – “we never went back to that house”. For other films, where the threat is totally neutralised at the end, the issue is that it might end on a non-horrifying note, without tension or worry; clearly, that’s not ideal for an ostensibly horrifying film. That’s why so many horror films end with a close up on the dead slasher showing a hand moving, or have the monster appear out of nowhere before a fade to black. It’s cheap and clichéd, but it gets one last squeeze of horror from the dried-up threat.

The bottom line is that horror has a structural weakness – it doesn’t last very well over a long period of time. There are obviously exceptions to this rule, but the longer a particular narrative extends, the less scary it is. Horror simply can’t be sustained – think of the countless series with progressively less-scary sequels.

In the end, horror boils down to threat. There has to be one – has to be some sort of lurking danger, some possibility that things won’t turn out okay. But as the audience and the characters get more information, survive for longer, that diminishes, until there’s no horror left at all.