I knew I was getting old when I got bored of metafictional games.

Case in point: I’m Still Here. Casey Affleck’s new film about his friend Joaquin Phoenix has been gestating for years – apparently, from even before Phoenix made news worldwide by announcing during a red carpet interview that he was quitting acting to pursue a career in hip hop.

It shows candid footage of the consequences of this decision: ugly early gigs, desperate attempts to work with a nonplussed Sean Combs, and endless scenes of Phoenix screaming abuse at his entourage. Drugs, girls, madness. You know: the usual.

Over nearly two hours, I’m Still Here reveals that its subject is A) a sucky rapper and B) a horrible human being.

Or is he? As I’m sure you know, almost all the buzz around the movie is of the ‘is it true or not?’ variety. Is this all a hoax? Phoenix gets angry when journalists suggest as much during the film, because the question implies his life is “a joke”.

Let’s take him at his word for a minute. What if this is an honest documentary? Well – in the words of one internet commentator featured in the film – it would be a sad story if Phoenix “wasn’t such an asshole”.

As the movie unfolds, however, it becomes more and more difficult to believe that what you’re seeing is true. And if I’m Still Here isn’t a true story, then what is it? It’s an elaborate, juvenile prank cooked up between friends to poke fun at the media. It’s not boring, exactly; it’s just empty. An astonishing amount of work for little effect.

In essence, it’s the story of an pretentious, self-obsessed actor who becomes a bad rapper. That sounds like a David Spade movie, right? (It would’ve been funnier if it was.)

Only the metafictional element, the mirrors-within-mirrors, the “oooh, are they playing a prank on Hollywood or is Joaquin just a loon?” that gives I’m Still Here any meaning at all. I think that’s why I found myself holding onto the idea that maybe, against all evidence, what I was watching could’ve been true.

It’s like Schrödinger’s Cat. A cat that’s alive isn’t much of a story, and neither is a cat that’s dead. It’s only fascinating before you open the box and the cat’s both alive and dead at once.

(I apologise for invoking the poor animal. It gets trotted out so often it must wish the waveform would just collapse and give it a 50% chance of welcome death.)

The best critique of the movie is embedded right in the middle of the movie itself: Phoenix’s infamous appearance on Letterman that unwittingly kickstarted I’m Still Here’s publicity campaign. Confronted with Phoenix’s bizarre appearance and behaviour, Letterman cracks jokes and tries not to roll his eyes.