Occasionally, the most compelling movies are those that defy simple explanations, resisting reduction to catchy taglines or concise plot summaries.

This certainly holds true for “If I Had Legs I’d Kick You,” a bold cinematic endeavor of the year, featuring Rose Byrne portraying a mother teetering on the brink. The film intriguingly unfolds with an unseen child suffering from a mysterious illness, the incessant whirring of medical machinery, and a peculiar ceiling hole that seems to take on a life of its own. Adding to this mix, A$AP Rocky appears as a motel employee, there’s a disconnected husband who communicates only via phone, and Conan O’Brien makes an appearance as an indifferent therapist. All these elements coalesce into a profound sense of exhaustion that spirals into mania rather than relief.

For the film’s creator, writer-director Mary Bronstein, the experience is akin to being on a roller coaster ride.

“Everything starts off as anticipated, but at a certain point, you notice the operator is missing, and the ride picks up speed, creating the sensation that you might just fly off into the unknown,” she explained. “I would describe it as an existential terror.”

Perhaps it’s fitting that the film, which is set to expand its release this weekend, emerged from an existential crisis. Seventeen years ago, Bronstein crafted the cult mumblecore classic “Yeast,” starring a then-unknown Greta Gerwig and the Safdie brothers. After stepping away from the film industry, she found herself in San Diego about eight years ago, where she rediscovered her passion for filmmaking amidst personal turmoil.

The result? A movie conceived in the unlikeliest of places—a motel bathroom.

The move to San Diego was not a happy one. Her 7-year-old daughter needed to be there for medical treatments and her husband needed to stay in New York for work.

For a disorienting eight months, Bronstein played the part of full-time caregiver while they lived in a tiny, dingy motel room. The only place she had to herself was their depressing little bathroom where she would go after her daughter was asleep and drink cheap wine and binge food under the awful glow of the overhead fluorescent lights. And she felt herself disappearing.

“My wants and needs didn’t factor into the equation. The task at hand was to get her better and to go back to New York,” she said. “And then this other thought started forming like, ‘Oh, wait a minute, she is going to get better. And we are going to go back to work. And then what the hell am I going to do? Who am I? It was a literal, actual existential crisis.”

That’s when it hit her: “I’m an artist,” she said. She started writing the script, her first since “Yeast,” in that awful motel bathroom.

A promising debut and a quick retreat

Bronstein came to filmmaking through performance, through the theater, studying at New York University’s Tisch and the Playwrights Horizon studio. But she quickly realized that she didn’t actually want to act: She wanted to be the one creating characters and working with actors.

“Yeast” was made in opposition to the films she’d seen on the festival circuit the year prior, with her now husband Ronald Bronstein, where she saw a lot of male fantasies of women on screen.

“It made me angry and I made ‘Yeast’ with that kind of rage,” she said. “I had never seen a film that reflected a very particular experience I had which is the trouble of navigating friendships from one stage of life to another, when boyfriends enter the picture, jobs and interests that have nothing to do with you.”

Like “If I Had Legs I’d Kick You,” “Yeast” was a pure expression of feeling. But when it premiered in competition at SXSW in 2008, it was met with a lot of hostility — especially from young male filmmakers.

It was a disheartening experience. Instead of soldiering on in an independent filmmaking community that didn’t seem to want her, she went away and did other things: She got a graduate degree in psychology, she had a kid, she ran an underground preschool in Williamsburg, and she wrote feminist theory for academic books.

In other words, she lived a life. And making films wasn’t part of it, for her at least.

Clawing her way back in

Bronstein’s husband is Josh Safdie’s creative partner who co-wrote and co-edited “Uncut Gems ” and “Good Time” as well as the upcoming “Marty Supreme,” which he also produced. And yet when she decided to write and make “If I Had Legs…”, she felt completely outside of any infrastructure or industry. She had no manager. No one was asking what she was going to do next.

But as with “Yeast,” she just knew she had to tell this story. And for the first time people willing to put money into making it happen agreed. The only creative concessions she made were logistical, she said.

O’Brien describes Bronstein as one of the most tenacious people he’s ever met. After he’d agreed to be in the film she told him that she was coming to Los Angeles and needed three hours a day with him for a week.

“There’s a part of me that’s thinking, ‘Really?’” O’Brien said. “I thought, ‘This isn’t really going to happen. She says that but we’re probably going to do an hour.’”

He was wrong, and glad about it. It was a week of intense character work that proved enormously helpful.

“She is so confident in her vision and she’s so confident about what needs to happen,” he said. “There are people that make movies because that’s their job and they just keep making them because that’s what you do. Mary is someone who has something to say. That, I think, really is the mark of a true artist.”

When the picture was locked, she texted O’Brien saying, “I made the movie I wanted to make.” That alone was enough: He was certain it was going to be great. Most audiences seem to agree too, from its festival run to its theatrical rollout, Bronstein has captured something about the zeitgeist, about motherhood, about the pressures of being a caregiver that gets under your skin and stays there.

“It was a very urgent expression that I wanted to capture in the film. I didn’t want that energy to die on the screen,” Bronstein said. “And I think I succeeded — maybe too much for some people, but for me, just in the right way.”

An overdue reappraisal and what’s next

Somewhere in the past few years “Yeast” has had its own resurgence, getting occasional screenings at art theaters around the country and abroad. The film had always had a few champions, including The New Yorker critic Richard Brody, but suddenly she noticed a fandom of 20-somethings emerging.

“They freak for this thing,” Bronstein said.

She’s not exactly sure why, but she has some theories about collective anger and the catharsis of seeing aggression on screen in a new way. Like many great filmmakers, she was, perhaps, ahead of her own time in 2008.

Now, she said, people are asking her “what’s next?” She has some ideas brewing. But she did promise one thing: This time, she said, it won’t take another 17 years.