When TV writer/producers are lured to the big screen by some more-money-than-sense studio — Amazon, say — they tend to fail and fail big in a couple of very predictable ways.

They try and cram in a TV season’s worth of story in a delicate 100 minute beginning-middle-end motion picture, like say, the fellow behind “The Sopranos” and the genius who got “Mad Men” on the air. No, they didn’t get to make second films.

Or they try to reinvent the medium, which is what the fellow who created “This Is Us” does, “freed” of the conventions of network TV and episodic storytelling and TV PG-language for “Life Itself,” one of the great cinematic boondoggles of our time.

Writer-director Dan Fogelman attempts an experiment in “unreliable narration,” when the storyteller is either mistaken or lies to the reader/filmgoer about what is happening, what has happened and for what reasons.

As if that doltish conceit wasn’t debacle enough, he also stumbles into the first pitfall, attempting to cram too many characters and too much story into an interconnected series of tragedies that befall loosely interconnected lives.

“This is Us” style, in other words.

The result is random, aimless and incoherent treacle — a movie which reaches for the heartstrings repeatedly, shows gruesome deaths that may or may not have happened, often from different angles.

But the creator of the weepy “This Is Us” only manages one moment that will tug at the heartstrings. And that involves a dog.

A false start gives us Samuel L. Jackson narrating and directing a script as an “unreliable narrator,” delivering the first of the film’s many misdirection plays. Oscar Isaac is the madman “hero” screenwriter behind that failed “script,” and he relates — to his shrink (Annette Bening) — the story of his great romance (Olivia Wilde).

The product of that romance, and the film’s stand-out performance, is by the angry punk singer daughter who is a product of that union, played by Olivia Cooke.

And then there’s the olive farm in Andalusia, Spain, where olive oil baron Antonio Banderas meddles in the life of his foreman and the foreman’s family and son.

The screenplay is filled with sequences where people say something, then we’re shown  “what they really said.”

Characters deliver long, personal history monologues — sometimes taking the person they’re telling their story to back to the day their met their great love, inserting themselves into the college library where they met, the accident they witnessed or caused, the day somebody died.

“I feel like my whole life is going to be marked by death and tragedy,” a little girl declares, except little girls of eight don’t talk like that, and the unreliable narrator at this point admits as much.

People talk of their world changing “at exactly that moment,” or another “completely random moment.”

Many — a great many — of those moments are mushy treacle. “Sometimes it scares me how much you feel.”

I am a fan of most every actor in this, and would never have bet they’d collectively collect checks in a movie as unwatchable as “Life Itself.”

Long takes drag us into a Halloween where our couple dress as Vincent and Mia in “Pulp Fiction,” another shows us Ms. Cooke (“Ouija,” “Ready Player One”) cover a song from Bob Dylan’s “Time out of Mind” “comeback” album. She relates how it was a favorite of her mother’s, fends off a “Lift your shirt!” heckler, tenderly applies herself to the tune on solo piano, and then thrashes through the rest of it, speed metal style.

Dylan shows up repeatedly on the soundtrack, singing or having that song cycle covered by characters.

And hell’s bells, none of it adds up to anything. “Life is the ultimate unreliable narrator,” with its randomness and endless mis-directions, isn’t a profound thought or theme to build a movie around.

It’s just something some gullible, poorly-read studio exec heard and thought, “I think I’ll spend Jeff Bezos’s millions on THAT.” The fool.

MPAA Rating: R for language including sexual references, some violent images and brief drug use

Cast: Oscar Isaac, Olivia Wilde, Antonio Banderas, Olivia Cooke, Annette Bening, Laia Costa, Jean Smart

Credits: Written and directed by Dan Fogelman. An Amazon release.

Running time: 1:58