He pulled into the driveway of a one-story ranch style house, ready for the day ahead. Wenner and his business and creative partner Chris Hillman were more than two years deep into a passion project, a documentary about grief. While the film featured interviews with a variety of experts, its beating heart was Wenner and Hillman’s personal experience with the emotion. Both had lost a brother to a heroin overdose; Wenner’s younger brother passed away in 2007, Hillman’s older brother in 2009.

The house belonged to Richard, Hillman’s father, who had agreed to be interviewed about his son’s death. The interview itself went well—Richard spoke eloquently and movingly. Afterwards, Hillman, Wenner, and a cameraman shot some B-roll. Wenner suggested that Hillman get in the frame, so they had footage of him with his dad. Hillman didn’t like the idea. The two men butted heads, with Wenner quickly standing down. By the end of the day, the minor disagreement was forgotten.

Or so Wenner thought, until he received an angry voicemail from Hillman, who clearly hadn’t forgotten anything and angrily ran through litany of complaints: the unprofessionalism of the shoot, errors made by the cameraman, Wenner’s inability to set a schedule and cede artistic control, and other ways “I had fucked everything up,” Wenner says.

In response, “I shut down. I let it ruin my whole day.” He eventually called Hillman back, and they got into a shouting match. Wenner hung up.

They didn’t speak for weeks. The documentary they’d poured hundreds of hours of work into, not to mention painful memories and emotions, hung in the balance. Both men wondered if this was how their partnership and passion project was going to end.

It wasn’t the first time they’d reached a breaking point.

***

Disagreements between business partners are so common they’re a trope. Think of a famous startup, and chances are good its co-founders have fought, one very likely pushing out the other for good. (See: Facebook, Snapchat, Twitter, SoulCycle, Tesla, among many others.)

While high-profile startup blow ups get the most attention—unsurprising, as millions, sometimes billions of dollars are at stake—any company or business partnership where two people are building something they care about is at risk of implosion if the relationship isn’t built on a strong foundation, says Howard Scott Warshaw, a Silicon Valley-based therapist who focuses on relationship counseling between spouses as well as co-founders.

This is true even for people who have known and liked each other for years before going into business, as was the case for Wenner and Hillman who met at conference in 2007 and kept in close contact before they started filming.

A friendship and a co-founder relationship are distinct, says Warshaw. He likens starting a company or artistic project to having a baby, in that it’s an exercise in self-discovery: “No matter who you’ve been up until that that point there are new parts of you that will emerge, that you and your partner have never seen before.”

This uncertainty—the feeling that you don’t really know the other person—is disquieting, particularly when it seems every wrong decision has the power to threaten the survival of the project. When the stakes are this high even minor disagreements can feel like a referendum, a dynamic that can pit co-founders against one another.

Wenner and Hillman were at an impasse. It wasn’t just the Pacific Palisades shoot. Leading up to the voicemail incident, they’d had a number of disagreements and weathered a series of escalating arguments. A permanent rift seemed likely.

Both men couldn’t believe they’d gotten to this point.

***

In the project’s heady early days, Wenner (who lives in NYC) and Hillman (LA) were in constant communication, excitedly running ideas by one another via texts, calls, and emails. “Sometimes we would talk for hours, just kind of, you know, feeding the the fire,” Hilman says. The documentary was a relief to both of them; having a partner lessened the fear of approaching a subject they had both been circling, alone, for a long time. Within a few months, they hired a crew and met in LA to begin filming. Progress was periodic. Over the next couple years, they would meet up for one to two weeks to film, slowly converting their ideas into footage.

At first, these meetings were largely conflict-free. From the outset, their roles were clearly defined: Hillman was responsible for nailing the artistic details. Wenner was the “big picture” guy; outgoing and friendly to Hillman’s sometimes prickly personality, he was also responsible for recruiting outside collaborators and experts.

What’s more, the two men had a strong mutual respect, borne of a shared loss and the understanding that came with it. For very long time, the importance of the work they were attempting—to help viewers work through their own grief by examining their own—kept disagreements from derailing forward progress. “Because of the emotionality of what we were pursuing was so deep, we had a jail get out of free card,” Hillman says. “Our vision and mission was so intense that I think we got away with certain aspects of our respective behaviors.”

But problems, instead of being talked out and resolved, were simply papered over. As the project dragged, tensions grew more frequent and harder to ignore.

Both began to recognize unsavory traits in one another that they had only seen in flashes. Hillman’s temper grated on Wenner: “He would get mad and yell and scream. Little things would set him off, and he would get mad at himself and take it out on me.”

Meanwhile, Wenner’s penchant for stewing rather than addressing problems frustrated Hillman, as did his tendency to view neutral comments as attacks. Before they began filming, “I had only experienced him as this warm engaging person who puts himself out there,” says Hillman. Wenner’s defensiveness and fear of direct conflict “made me start to doubt him a little bit.”

These issues first came to a head a few months before the Pacific Palisades shoot when Wenner forwarded Hillman an email, in which a prominent researcher on grief who initially seemed interested in participating declined to be interviewed. Hillman responded by asking questions about how Wenner had approached the researcher, which Wenner read as criticisms. He responded with angry defensiveness. Hillman, who was traveling at the time, dramatically escalated the situation, responding with a curt, emailed: “Fuck you bro.”

They eventually smoothed things over without talking through any of the underlying issues. For Warshaw, that’s a red flag. “Founders who can’t communicate well and form a good bound — that can guarantee failure,” he says. When a shared history is fraught enough and there is no system in place to address conflict, seemingly minor misunderstandings are capable of reopening old, nasty wounds.

“It’s often not really about what’s happening in the moment, but the weight of accumulated resentment,” Warshaw says. “What people tend not to do is take responsibility for the resentments they created by miscommunicating in the first place.”

***

Miraculously after the voicemail incident, Wenner and Hillman were able to do exactly that. After a week, Hillman extended an olive branch. The gap between the actual issue at hand and their response to it scared them both enough to take action. The film was too important for them to continue on like this.

And so each combed through past conflicts with a critical eye to his own behavior, uncovering unsettling truths. Wenner noticed a passive aggressive slant to the way he handled conflict: “I wasn’t telling him how I really felt. I was holding everything back, and my story was, oh he can’t handle it, he can’t hear the truth when really he needed that more than anything.”

Hillman, in turn, saw an anger problem. He had a tendency to lash out when frustrated or challenged, and Wenner was often on the receiving end of his temper. Tension erupted into full-fledged fights when Wenner, after weeks, sometimes months, of swallowing his feelings, stood up to Hillman or tried to set boundaries. Hillman pushed back, which triggered an outpouring of resentment from Wenner, which set Hillman off further, causing Wenner to retreat. It was a vicious cycle that lead to long stretches of time when the two men stopped speaking, halting production.

They went through past conflicts, analyzing their interactions to identify breakdowns in communication and what they needed to be aware of and change going forward. It was a valuable exercise. Wenner now tries to work past his discomfort to voice his concerns, even minor ones, before they can morph into potentially schedule-stopping disagreements. He also stops himself from immediately reading Hillman’s blunt style as a critique. For his part, Hillman keeps tab on his temper and takes a breath when he can feel himself spiraling out of control. He also takes pains to encourage Wenner to voice his opinions and refrains from steamrolling them with his own. “Eighty percent of our fights is because one of us doesn’t feel heard,” Hillman says. “What we are fighting about becomes irrelevant.”

There is still conflict, especially now, as work on the documentary winds down and they prepare to enter it in festivals. Neither men are completely transformed: Wenner still tends to repress his emotions, Hillman remains a hot head. But both say they have a better understanding of how the other communicates, which means misunderstandings can be caught before they can turn into something more insidious.

“We’ve learned to talk through it,” Wenner says. For a different project, both say they might not have reached this point. Honest self-reflection isn’t a fun way to spend a Saturday afternoon, nor is a process that ever really ends. But for two people who want to work together to build a partnership and product that lasts, it just might be essential.