We will never get a movie like The Blair Witch Project again. Having said that, we’ve had dozens of movies like The Blair Witch Project. In the 20 years since its release, it has transformed the horror landscape, and more besides. “Found footage” is now a sub-genre in itself thanks to it. How many horror movies have we seen claiming: “This all really happened, honest”? How many occult symbols and folk myths have crossed our screens? How many gung-ho teens have set off on an adventure, never to return? And how many times has a gimmicky horror reaped rewards for virtually no outlay? Blair Witch did not invent all these tricks but it put them together to create a phenomenon. It is the 21st century’s Exorcist.

One of the reasons we will never have a Blair Witch Project again is because we’ll never have an early internet again. Going viral was difficult in 1999 – we barely had broadband, let alone social media – but it was also a time when people actually believed what they read on the internet. The marketing campaign started before filming had even begun: creators Daniel Myrick and Eduardo Sánchez made a short documentary to show to investors, presenting the mythology and the disappearance of the story’s three student film-makers as if it were a true story. They took the same approach online, creating fake websites, TV news clips, newspaper and police reports, interviews, journals. The website went live in June 1998, six months before the movie premiered at Sundance, where the makers handed out missing-persons flyers.

And it worked: many early cinemagoers thought the film was a documentary. It is still one of the most delectably scary movies out there, and its ingenious premise required it to break all the rules: no script, no jump scares, no music, no professional crew, no special effects, not even any witches. What it did have, which often goes unremarked upon, was totally convincing actors. Horror is traditionally about confronting our darkest fears but Blair Witch doesn’t really do that; instead, it shows us other people confronting theirs. The hysteria is contagious.

It could never happen again, though (the makers of A Cure for Wellness were forced to apologise for creating bogus online stories to promote the film). Looking at our current post-factual soup of fake news, conspiracy theory, bogus mythology and untrusted sources, trust in “stuff you read on the internet” is at an all-time low. Could it be that someone noted the efficacy of Blair Witch’s viral campaign, based on falsehood, fear and gullibility, and decided it was too good for simply promoting movies? Maybe Blair Witch shaped our political landscape as well as our horror one. Maybe the curse was real after all.