The Blair Witch Project landed like a guerrilla invasion force in July 1999, on a feverish tidal wave of ingenious nascent-Internet publicity. It hit multiplexes just in time to obliterate the preening bloat of Jan de Bont’s The Haunting, which cost more than 250 times as much. By the time it came to home video, Dan Meyrick and Eduardo Sanchez’s unassuming, five-figure-budgeted little campfire ditty possessed the greatest cost-to-profit ratio in the medium’s history, a record it still holds.

But why was America, if not a good part of the filmgoing world, seduced by this pro-am goof? That is the question the film’s reputation, now largely confined to jokes, cannot answer. Most of the voluminous discourse inspired by The Blair Witch Project hasn’t revealed a substantial clue as to the film’s gravitational pull, instead focusing on the fictional backstory (most of which—interviews, fake news footage, etc.—was contrived as part of the original mock-doc project and then used only as part of the promotional barrage), the actors (how much did they know in the woods and where are they now?), and the ever fascinating production tale: the movie was shot almost unplanned and without the presence of the filmmakers, as if it were just a few centimeters from an actual home movie. Of course, its box office boom in spite of its humble origins became the largest part of its trailing story.

But it’s still a horror movie, not just an industry story, and its relationship with its sinkhole-fraught genre is the first place to start shopping. "Horror"—a clumsy emotional-code label that essentially signifies any narrative text that a) aims to disquiet the consumer to some degree and b) does so via "supernatural" or often just ultraviolent material—has been as abused and watered-down as any other major genre, to the point that the innate and express potentialities of horror films have mutated into little more than a hectic barrage of noise, special effects, and savagery. (All of which rarely if ever shocks or "horrifies" its teen-to-geek demographic, instead generating or at least promising derisive laughs and feelings of cultish superiority). Still, the genre has retained its potential for catharsis and discombobulation, and audiences swarmed in droves to Blair Witch at the very suggestion that they might have a genuinely dangerous, or at least discomposing, time at the movies, that here finally was a horror film that jeopardized the placid semi-numbness of their viewing experience and that discovered something new they had apparently hoped for but never encountered: a cinematic engagement that by its formal nature unhinged their defenses.

Horror films can contain juicy subtextual shank meat, but how often do they actually provide the visceral experience they promise? To say Blair Witch is an emotional experience says everything—there’s nothing to it except the devilish, high-octane Fun Factory of don’t-knows and whatzzats; no text, no plot, no layers. It’s raw tumult, conceived so beautifully it could allow itself to be executed sloppily, and the result is a movie-audience relationship that, perhaps for the first time, seems to be less a relationship than a trial, an ordeal by light.

Even as the months and years passed, and the film became familiar, safe, and ridiculous to us (just as actual hazardous experiences do), the memory of seeing it for the first time, early in the hype hurricane if you were lucky, is still there, out of breath. (The lucky ones who saw it at Sundance, not knowing a thing about it, at the legendary late-night showing and then emerged into the mountain nighttime, could make millions bottling that experience.) The film’s influence has been oddly attenuated: the subsequent uses of the trope—[REC] (2007), Redacted (2007), Cloverfield (2008), Quarantine (2008), etc.—took years to start propagating. Cinema is an industry of procedural habit, and the childish simplicity of Blair Witch may have seemed too radical a break with tradition. But the recent spate of mock docs have also undoubtedly been nudged along by the new ubiquity of cell-phone cameras, as well as by the pervasiveness of DIY Iraq war texts in the form of infantryman blogcasts, cell-phone reporting, embedded IM dispatches, and rogue documentarians, as if the war itself was staged for the benefit of personal-communication hardware. It’s easy to be jaded by this time, and those later movies all have the air of technological cynicism about them. (They haven’t managed the necessary low-budget conviction, either.)

But it’s important to remember Blair Witch at its first blush—few films are as fragile in the face of reviews and reviewings—because it formally redefined the possible engineering of horror films (from contrived tall-tale spectacle to raw subjective tribulation) and because that re-engineering has significance beyond genre and entertainment. It’s cinema in its primordial form.

What’s being stripped away here, like layers of civilized underclothes, is traditional film syntax, which evolved over the first decades of the medium by virtue of its natural tendency to provide narrative information in a syncopated, reassuring, even anesthetizing fashion. This syntax, the industry’s bread and butter from 1903 onward, is the reason why, if you ask a 21st-century college student about a film, you will hear about content, not form—it never occurs to the massive majority of film consumers that the experience they’re having in their seats might have as much to do with how as it does with what. The syntax system is, famously, successful when it is invisible, when the literal context and intent of how a movie is made disappears and the viewer "escapes" into an alternate world-tale, in which they can half believe they’re passively involved, but which they always know is an artificial contrivance under the firm control of an elaborate, costly storytelling apparatus. Active participation is kept to a minimum; ordinary movies are usually consumed in a sort of bipolar trance, snacked upon by your left lobe while your right lobe naps.

This contradicts the implicit intent of the horror genre, which is geared toward discomfiting or upsetting or shocking the viewer and has over the decades produced a unique tension with the syntax of cinema itself. From The Cabinet of Dr. Caligari (1920) onward, the films have, in a manner of speaking, been colluding with the enemy, trying to cater to its own opposite mode, and as a result the genre has been popularly pigeonholed as kids’ material. The occasional landmarks—like James Whale’s Frankenstein (1931), George Romero’s Night of the Living Dead (1968), and William Friedkin’s The Exorcist (1973)—have succeeded in picking their viewers’ psychosocial scabs by way of unearthly spectacle and queasy ideas of irrational chaos, all of it utilizing classic syntax while surmounting its mollifying effects in ways most horror movies cannot manage. For many intents and purposes, Blair Witch changed the game. These days, a horror film that detours around the question of safety-first syntax is fighting a losing war, in which the Dolby soundtrack blam might be Hollywood’s lamest shot fired. Since the codes of narrative filmmaking imply that we will unambiguously receive all pertinent information, it stands to reason that a horror film should do the opposite: withhold information, leave you uninformed, contrive to be at least partially without control over its own visual narrative. When you’re watching a movie, you’re in its hands; what if those hands were unsafe, sweaty, uneasy about what they know?

Blair Witch is the nec plus ultra of this notion—a film semi-literally shot by panicked, stranded, hyperventilating cameramen alone in the night. (As the story goes, the three stars went into the woods with little foreknowledge and without a script, and baskets with instructions and fresh batteries were planted for them at staggered locations. The objects and incidents they encounter were all surprises, as was the forest footage to the filmmakers when they looked at it and saw that their concept had been spontaneously fulfilled to a degree they hadn't thought possible.) Film audiences are like trial juries—we sometimes have to rely on unreliable testimony and circumstantial evidence (read: editing-room sutures, special effects, etc.), but the only thing that’s not suspect is undoctored footage. This transgressive legacy streams back to the Lumières and the basic, Kracauerian/Bazinian idea of cinema’s import belonging primarily to its utility in recording real life, in real time. Fear is not a state easily conjured by obvious fakery. There’s a basic, physiological factor at work here as well: vision itself, when it’s framed, is an anxiety engine. Try walking around an unfamiliar house or office with a camera pressed to your eye—because of the constrictions placed upon the viewing field by the frame, simply turning a corner creates a sensual dread, a helplessness that the coded syncopation of movie narrative has worked to inoculate ever since The Great Train Robbery. (Stanley Kubrick tasted this effect with the floor-level Steadicam roamings in The Shining.) When the cameras in Blair Witch lack focus or sufficient light or a hand steadied by professional control, the direct effect on us is a sense of panic more like a very bad dream we cannot wake from than watching a manufactured product we can trust to bring us home comfortably. Less is not only more; it’s a completely different act.

Blair Witch’s subversion of the system succeeded where decades of alternative films have not: in interrogating, or at least unsettling, our universal sense of civilized control and our social presumptions. (Indeed, the most significant predecessors might be Alan Schneider and Samuel Beckett’s Film, from 1965, and John Lennon and Yoko Ono’s Rape, from 1969.) But it may be that mass audiences prefer the knockout-drops of blockbusterdom to the nerve-wracking experience of subjective risk, despite the popular declamations about rollercoaster rides. In 1999 and since, many viewers ended up finding Blair Witch ineffectual, chill-less, and laughable—in what appears to be a common defensive posture, ignoring the fact that the horror genre, like musicals and comedies and magicians’ acts, requires an innocence of heart and a readiness to engage. Unsurprisingly, the film’s uncompromised attack can trigger a fight-or-flight response, which is to say that cinema itself, at its pre-mediated, pre-commercial roots, is not an innocuous entertainment but a return to a primal unknowing.