M. Night Shyamalan has not been sleeping well. This month sees the release of Glass, the final installment of his Eastrail 177 trilogy, which began nearly two decades ago with Unbreakable, and received a late, surprise follow-up with Split in 2016. While I understand feeling excited anticipation for the release of Glass, I’m confused by the source of Shyamalan’s anxiety. Of course, since becoming a household name with the classic supernatural horror The Sixth Sense, the director has had a notoriously rocky relationship with critics. But Unbreakable was a critical hit, and not only did Split receive generally good reviews, it also grossed over $278 million worldwide, on a budget of $9 million. Somehow, I think Glass will do just fine.

Though, to be fair, I didn’t personally invest millions of dollars in Glass – Shyamalan did. And now he’s waiting to see if his gamble paid off.

“It’s very scary and unnerving and hopefully in ten days I’ll be able to sleep properly again!” says the filmmaker.

He’s had sleepless nights before. Split was also a personal passion project for Shyamalan, and he similarly funded much of it personally in order to keep creative control. But after Split’s phenomenal financial success, studios were ready to throw cash at him. Why take all the risk and stress upon himself – again?

“It’s about taking away a safety net,” says Shyamalan, who likes his cast and crew to call him ‘Night’. “When there’s no way out and it’s yours, you don’t think of anything casually. I’m on every detail. I’m not fun on my sets, I’m obsessive over every detail. You become hyper invested when it’s all yours. Also, when you take money from a studio, they have the right – and I’m not talking legally, but morally – to say, ‘Hey, I don’t think you should do that, that’s too weird!’ They’re allowed say ‘No, don’t crush an old lady!’ or ‘I don’t think he should eat the girls, can he not eat the girls?’ So it’s not meant to be gambling, it’s meant to be purifying. And I’ve found more money certainly doesn’t make better art.”

Nor does excess – a lesson he hadn’t quite grasped when he originally conceived of the Eastrail 177 story. He wanted to cram all of his ideas into one film, as Elijah Price (Samuel L. Jackson) orchestrated a train crash to make David Dunn (Bruce Willis) realise he’s a superhero. That came just in time for Dunn to fight Kevin Wendall Crumb (James McAvoy), a man with multiple personalities who has kidnapped three girls – who watch the battle, survive and tell the world that superheroes exist.

So… it was going to be a seven-hour movie?

“Longer than that!” laughs Shyamalan. “But I realised I needed to break it up into two or three parts. Not because of the length, but because of the narrative structure. Once you put the girls in danger, you can’t have a character piece on the side. You can’t have him having an existential crisis - the audience would be too impatient, shouting ‘Accept you’re a fucking superhero and go save the girls!’ So I split up the characters. Unbreakable became the first act, Split became the ticking clock installment, and now Glass has the philosophical, winking tone of Elijah.”

Winking it is. A genre-riffing film filled with meta moments, Glass explores the tropes and conventions of comic books and their cinematic adaptations – something audiences are much more fluent in now, compared to 20 years ago when Shyamalan first conceived of it. Why does he think that cultural shift occurred, where we’re now flocking to comic book stories – some of which we’ve seen before?

“Audiences need familiarity right now in a very unique way,” he opines. “In the ’90s, we didn’t need that – you could barely get a sequel made. But now, everything is a sequel or a reboot. It’s a cultural thing. People want to feel connected, and they want to feel safety. They want to know what they can expect. Framing is really important to them right now. And maybe that will change, and we’ll move back to original movies. And comic books are stories about the power of regular people saving us, becoming gods amongst us. How titillating is that? Something I touch on very tacitly in the movie, is that these are the opposite of the stories of powers outside of us. And that obviously appeals to audiences right now.”

Glass sees David Dunn, Elijah Price and Kevin Wendall Crumb institutionalised by a psychiatrist (Sarah Paulson), who tells them that they are all suffering from the grandiose delusion that they are superheroes, when they’re just ordinary men. The struggle between each of the characters’ self-belief and self-doubt plays out onscreen, and I wonder if the director is working through his own relationship with those feelings?

“Yes, the central question is about me and my journey in life,” he nods. “Not necessarily just about my relationship with my films and critics, but in relation to just generally believing in myself and struggling with doubt. But it’s a ubiquitous thing – that universal question of, ‘Am I good enough, am I worthy of anything?’ Then we get told what we are and what we’re not from all these external forces. So the movie is about that movement into a philosophy of embracing both. The people in the movie who are doubting are right. And the people who believe are right. We are both ordinary and extraordinary, and they can co-exist.”

Glass is in cinemas now.