Art directly imitates life in Chloe Zhao’s “The Rider,” an elegiac, ruminative modern western about a young South Dakota rodeo rider who must decide what choices to make after suffering a serious head injury that threatens to end his career on horseback. Straddling the line between fiction and documentary, the film offers a portrait of Brady Blackburn, who is played by Brady Jandreau, a twenty-year old of Sioux background living on the Pine Ridge Indian Reservation whose love of riding has, in fact, been endangered by a fall. And his father Tim and Asperger-afflicted sister Lilly are portrayed by his real dad and younger sibling.

There’s isn’t much plot to “The Rider.” Brady bickers with his father, whom he considers a failure for having wasted money on gambling. He has sweet moments with Lilly. He visits a friend (Lane Scott) who was permanently disabled in a riding accident and now lives in a rehab facility. He takes a temp job as a clerk in a drug store. He goes out with his rodeo pals, who encourage him not to let the accident deter him from getting in the saddle again and engaging in those moments of dangerous action they all so love.

This result is an incisive cinematic portraiture of a young man at a critical crossroads in his life. What narrative there is arises from Brady’s efforts to get back into shape to compete, even though his physical impairment—he can barely control his right hand—is obvious. A natural horse whisperer, he’s asked by a local rancher to break some of his stock that have resisted all the efforts of others to bring them to heel, and manages to succeed with patience and kindness. And eventually, with his father’s help, he purchases a troubled horse than he believes, with work, can be trained and ridden. Eventually he goes back to the rodeo, intending to ride, even though a single fall could put him in the same condition as Lane and his father says that he’ll just be killing himself. What will he ultimately decide?

That decision is, in the end, the central issue of the entire film; every aspect of the story that Zhao—who reportedly met Jandreau before his accident and crafted her script afterward—contributes to it. During an employment interview, for example, we learn that Brady does not have a high-school diploma; to what extent does that limit his choices? It’s obvious that he feels an obligation to care for Lilly; what would become of her if he were in Lane’s condition? Is there a middle road that he might take, one that wouldn’t involve rodeo riding but could allow him to work with horses in some other capacity? The film raises all these matters, but in an indirect, subtle fashion.

In support of that approach, Zhao’s method is quiet and undemonstrative. The film luxuriates in the South Dakotan spaces, with Joshua James Richards’ widescreen camerawork careful to take advantage of the beautiful, but desolate locations. Alex O’Flinn’s editing contributes to the unrushed mood, as does a lovely, spare score by Nathan Halpern.

But the key to the film’s impact is the lead performance. Jandreau occasionally seems uncomfortable, as one would expect of a non-professional playing a version of his own life, but he projects a committed, convincing image of the sort of broodingly uncommunicative figure we can visualize as coming from this impoverished, hardscrabble milieu. It’s painful at times to watch Brady, but at the same time he makes you admire his grit and determination. The supporting cast, most of them non-professions too, add to the sense of authenticity.

“The Rider” moseys rather than galloping, and it takes patience to appreciate its virtues. But it’s worth letting Zhao’s vision work its magic on you.