When a movie arrives with a title as unusual as “The Peanut Butter Falcon,” we expect a scene explaining why it’s called “The Peanut Butter Falcon.”

There has to be a legit reason for such an odd pairing of popular food spread and bird of prey, right?

Sure enough, we eventually find out where the title comes from, in one of the most unabashedly corny scenes in a movie dripping with sentimentality to the point of occasionally docking in hokey territory.

But that’s OK, because by the time that sequence occurs, “The Peanut Butter Falcon” has already forged a well-established identity as generally warm-hearted and sweet-natured take on “The Adventures of Huckleberry Finn,” and I had come to accept the sometimes reality-defying, storybook approach to the material.

‘Peanut Butter Falcon’: 3 out of 4 CST_ CST_ CST_ CST_ CST_ CST_ CST_ CST_ Roadside Attractions & Armory Films present a film written and directed by Tyler Nilson & Michael Schwartz. Rated PG-13 (thematic content, language throughout, some violence and smoking). Run time: 93 minutes. Opens Friday at local theaters.

Zack Gottsagen, an actor with Down syndrome, delivers funny, moving and consistently strong work as Zak, who has been abandoned by his family and has been housed an old-age facility in North Carolina because there’s no place else for him to go.

Zak is obsessed with an old VHS tape featuring the professional wrestler known as the Salt-Water Redneck (Thomas Haden Church), and he is determined to break out of the facility and make his way down to Salt-Water Redneck’s camp, where he can realize his dream of becoming a professional wrestler.

With the help of his crusty old roommate Carl (the one and only Bruce Dern, the go-to choice to play a salty old-timer in many a movie), Zak actually does escape — but given he’s clad only in his underwear, has no money and doesn’t know a single soul in the outside world, navigating the few hundred miles to Salt-Water Redneck’s wrestling school seems about as attainable as flying to the moon.

Until Zak crosses paths with a no-good troublemaker on the run, who reluctantly agrees to take Zak along with him. Now the odds of Zak realizing his dream have soared from zero percent to maybe, well, 1%.

Shia LaBeouf turns in one of the most sincere and effective performances of his career as that aforementioned troublemaker: a law-breaking, self-destructive fisherman named Tyler, who has been on a downward spiral ever since the death of his older brother (played by Jon Bernthal in flashback sequence).

Tyler and Zak become unlikely partners on the lam, although their respective pursuers, while equally dogged, have markedly different missions. The revenge-minded fishermen hunting down Tyler have no qualms about beating him senseless or even killing him, whereas Zak’s caretaker Eleanor (Dakota Johnson) is hoping against hope she’ll find and save the helpless Zak before something terrible happens to him.

Ah, but perhaps Zak isn’t so fragile and dependent and helpless after all. The hard-boiled Tyler can’t help but be worn down by Zak’s infectious enthusiasm and unfiltered observations. But throughout their journey, whether they’re facing great peril or having fantastic adventures involving booze and a gun and a Bible-thumping old blind man, Tyler refuses to coddle Zak or make excuses for him or treat him like a child.

It might be the first time in Zak’s life someone keeps telling him what he can do instead of constantly reminding him of his limitations.

“The Peanut Butter Falcon” keeps amping up the Whimsy Factor, with Tyler and Zak building a raft and sailing to their destination, and Tyler and Eleanor striking up a most unlikely (but endearing) romantic relationship.

Not that there aren’t some harsh and heavy injections of reality intermittently puncturing the sun-dappled fable. The bad guys in this movie are truly bad, and it’s no guarantee everyone will get out of this journey alive and uninjured.

Tyler brings out the rebel and the spirit of adventure in Zak and Eleanor — but he’s the real winner in the exchange, because they’re bringing out the best in a man who had just about given up on doing anything valuable with his life.