Virtual reality revenue will explode more than tenfold over the next four years — to some $75 billion worldwide in 2021, according to one recent forecast.

I’m sorry, what? That’s just virtually insane.

The delirious growth expectations for VR are triggered by investments by the likes Facebook, Samsung and Google, which made several VR announcements this week at its annual I/O developers conference, among others. If they’re spending billions on this stuff, there’s gotta be a market there — right? But I think the fantastic projections for VR’s prospects amount to the tech industry huffing its own hype fumes. There are several roadblocks to VR becoming a big business, and none of them will be easily overcome.

Virtual reality makes for a fantastic demo, and it’s become an au courant accoutrement at film fests. At the Cannes Film Festival this week, Alejandro G. Iñárritu is showing his VR documentary on illegal immigration. The director said virtual-reality filmmaking represents “an art in itself.”

Sure, it’s a groundbreaking new frontier and, for some, an exciting new canvas to work on. But in the everyday, relax-and-unwind real world? I just don’t see a VR future as envisioned for us by Silicon Valley’s engineering brain trust making major inroads in the living room. We’ve seen a version of this movie before: 3DTV, which was hamstrung by the same clumsy headgear and lack of compelling content.

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I would wager that for most regular people — i.e., not tech types or bleeding-edge creatives — VR doesn’t pass the must-have test.

Bellying up to the VR bar requires too much effort. It’s an investment in time and money for something that — let’s be honest — you’re really not going to use much. (Unless you’re like these two guys, who last month set the Guinness World Record for VR binge-viewing at 50 hours.) Vertical wind tunnels for indoor skydiving are cool, too (as are, say, IMAX screens) but it doesn’t make sense to have those in my house.

More to the point, VR’s immersive, solitary confinement simply doesn’t square with how people consume entertainment at home. Never mind that you can’t interact in-person with another human being with a Google Daydream, Oculus VR or Vive headset strapped to your noggin. We need our field of vision free in order to continually glance down at our smartphones: According to Deloitte’s 2017 “Digital Democracy Survey,” 99% of millennial and Gen Z viewers engage in an average of four other activities while watching TV (such as texting, using social networks, reading email or shopping).

Then there’s the fact that VR requires a caffeinated level of engagement. You have no choice, locked in the cage of a VR headset, but to pay constant attention. It calls to mind the behavioral-modification scene in Stanley Kubrick’s “A Clockwork Orange” where Alex’s eyes are kept pried open.

To me, it feels like work. In traditional visual storytelling, the whole reason to have directors and editors is to provide a (literal) point of view. VR demands that you, the viewer, take on those duties. In a virtual-reality experience, I’m always anxious that I’ll miss something important if I’m not looking the right direction.

Traditional TV shows and movies, the killer apps of home entertainment, are non-interactive at a storytelling level — and people like them that way. Your average American doesn’t want to expend an undue amount of brain cycles concentrating on watching a baseball game or “The Big Bang Theory.” But what about video games! you may exclaim. Yes, that is a form of interactive entertainment that’s a gigantic business, and VR has specific applications in that segment.

The question is: How much does a virtual-reality environment enhance the power of storytelling? I’ve seen dozens of VR experiences over the last few years, and I always come away thinking that I’d have enjoyed it more on a traditional 2D screen.

Meanwhile, I haven’t yet talked about how goofy VR headsets look on people.

Maybe I’m wrong. Maybe VR will catch fire once really amazing stuff that takes advantage of these platforms produces some truly unique experiences. I’m generally skeptical, though, when there’s a Shiny New Technology Thing that’s supposed to knock my socks off. Take, for example, the hypothesis by Twitter and Facebook that conjoining live sports with social interactivity into one screen is just amazeballs. Last year, I criticized Twitter’s implementation of live-streaming video alongside a torrent of tweets as a “distracting mess” — and was called an oldster who just didn’t get it.

I am a lot more bullish on an area that often gets paired with VR: augmented reality, which superimposes virtual stuff into your real-world view. We have already seen major AR hits in the form of Pokemon Go and Snapchat’s selfie filters. Facebook is bulking up on AR, too. CEO Mark Zuckerberg said he used to think augmented reality would require special-purpose glasses. Unlike VR, of course, it doesn’t.

As for VR, I understand why there’s enthusiasm for this new way to experience video content. It’s often fun. And it’s also exhausting and, at the end of the day, too big a commitment for your average consumer.

VR probably has a great future as a segment of the video-game business; as a training tool; and at events and entertainment venues. IMAX believes VR has a future in the cinema, just as 3D movies in theaters do today. But even there, how big can virtual reality really become? I don’t see how VR can deliver enough bang for the buck to ever become a mass consumer market.