Sympathy. It’s one of the unspoken rules for crafting a film that works. Not that viewers have to actually like the film’s protagonist(s), but they do have get close enough to relate to them on some level, however minute, be they mean girls or serial killers. That said, rules are made to be broken. Still, keeping an audience sitting still for two hours just to follow characters they don’t have a smidgeon of sympathy for takes a rare master’s hand. Director Wim Wenders, though a most venerable master, fails to pull this off in “Don’t Come Knocking.” But the bigger problem is that it’s unclear whether the film consciously tries to break the rule in the first place.

It’s a story of the American West and broken family ties, two of the German director’s relentless obsessions. (See him at his apex in 1984’s “Paris, Texas” for a fine mix of both.) “Don’t Come Knocking” revisits the reliable ol’ American Dream with a pastiche of symbols — Hollywood big-shots, classic diners, glittering casinos, cowboys galloping through the desert, ’50s cars barreling down lonesome highways. In short, a European’s wet American dream. Writer Sam Shepard, also an actor and virtuoso playwright who proved his screenwriting skills with “Paris, Texas,” arranges this all to fit in the present day by casting an aging cowboy-film star (Shepard himself) as the failed protagonist.

So much for making your own role. Shepard’s got the perfect gruff, weather-sculpted face, but the cringing starts at the first lines of dialogue and never lets go. Howard is an over-the-hill movie star, treated like a household name by most but bizarrely unknown to those for whom it’s convenient (the son he never knew he had). At this arbitrary point in his hedonistic life of drugs, women and scandal, Howard disappears from the set of his latest Western. He gets to do the scenic cowboy-riding-through-the-desert photo op for a few minutes before he switches to more convenient modes of locomotion. Destination: his roots. His mother (Eva Marie Saint), whom he visits first in Reno, painstakingly beats into the viewer — because Howard, stone-cold, doesn’t seem to register — how strange it is to see him after so many years of abandonment. But apart from learning through a casino scene that Howard is an annoying, violent drunk, we still see next to nothing of what lies behind the leathery mask. Too bad, because the casino is stunningly shot — mirrored ceilings reflect the swirling, heady lights, leaving the viewer feeling drunker than Howard; but here, like in the rest, the film works best when everyone shuts up.

Hopes spring wild when his mother conveniently remembers to tell Howard that a woman called many, many years ago about some son of his in Butte, Mont. But when he gets there, he only digs himself a deeper hole by half-heartedly trying to get back into the life of Doreen, his ex (Jessica Lange, giving the script her very best shot). What does Howard really want? Who the hell knows. Doreen, like Howard’s mother, is a subservient, patient woman; both seem much too intelligent to bother with Howard’s antics, yet search tirelessly for what they believe is a tortured soul buried in him. If only the viewer could see what they see.

Adding to this obsession over Howard is a detective (Tim Roth) sent out by the actor’s Hollywood bosses to force him to fulfill his contract. By some odd logic, the stern detective is painted as a gigantic stereotype — cold, rude, foreign and meticulous to the point of having OCD. He’s a pointless plot device, providing one of the most unintentionally hilarious moments of the film when he clicks his electric shaver on and off over the dead silent desert and asks, “Is anyone there?”

Then, to complicate things further, come the youngsters. They’re a nice diversion, but none of them ring truer than the last. Sarah Polley fits the film’s female mold as yet another unknown offspring, who takes pity upon Howard while she stalks him, all the while holding an urn containing her mother’s ashes under her arm (the urn mainly serves for her to talk to in a great “tell-not-show” exposition of the improbable plot turns.) Then there’s Howard’s son by Doreen, Earl (Gabriel Mann), and Earl’s insane girlfriend (Fairuza Balk, who does a creepy remake of her I’m-so-quirky-and-crazy-and-bug-eyed-who-knows-what-I’ll-do-next persona from “The Craft”.) Earl, though he’s never met his father and has a lovely mother, seems out to prove that machismo and violence is genetic, picking fights and throwing the entire contents of his room out his second-floor window and into the middle of the street. (In a movie where suspension of disbelief is required here and there and everywhere, neighbors don’t exist.) Guess how the inevitable father-son meeting goes down. If your guess is along the lines of “You’re not my father; I never needed a father,” you’re close enough. But the key to a manly father-son reconciliation in the wild west is, of course, to give the son the keys to that classic car.

Earl does provide Wenders with a nostalgic interlude, thankfully. The boy can sing and does a smoky-bar performance eerily mirroring the concert scene in Wenders’ 1987 masterpiece “Wings of Desire.” Butte, Mont. is no ’80s underground Berlin, and Mann is no young Nick Cave, but it’s a nice touch reminding all the more of what could have been.

The cast also has to get credit for fighting through their lines. Shepard’s script would have sounded forced even on the stage; on screen, it’s too often laughable at the (ostensible) height of drama. Hear Doreen and the estranged daughter, who’ve just met: SKY — “I think I like the movies better.” DOREEN — “Than what?” SKY, in hushed tones — “Than real life.” Or even better is Doreen hysterically yelling at Howard on the street: “You’re a coward, Howard! That rhymes, doesn’t it?”

Viewers, with hardly any insight into the wooden Howard, are left with a closing image of the three youngsters driving Howard’s old car past an ominous road sign that reads “Divide – 1; Wisdom – 52.” For most of the movie the viewer is left asking “Are we there yet?” But when we finally are there, there is still a long, long way to go.