From outside appearances the two companies seemed well aligned as Cruise ramped up and soon began testing self-driving Chevy Bolt electric vehicles in San Francisco and later, in Scottsdale, Ariz.

But relationships are complicated and messy. It turns out that the transition from small startup to subsidiary of one of the world’s largest automakers wasn’t so effortless, Kyle Vogt, CEO and co-founder of Cruise Automation said on stage at Fortune’s annual Brainstorm TECH event in Aspen, Colo.

“Working inside of a large company has not been smooth sailing,” Vogt said on stage at the Brainstorm Tech event. “It took us probably six months to a year to really figure out how to work well together and to achieve what we have now, which is mutual respect.”

Vogt admitted that he and the rest of the Cruise employees were probably viewed as the young jerks walking into GM and telling people how to do their jobs.

“I’m sure some people thought that at first,” Vogt said in response to a question from senior writer Erin Griffith. “It probably went way too far in that direction when we first got started.”

That has since changed, as employees at the once-small startup and the giant automaker recognized and respected the expertise that each company brought to the relationship.

“We identified that the folks with decades of experience building cars really know what they’re talking about when it comes to assembly plants and how they put things together,” Vogt said. “Over time I think we’ve developed a mutual understanding and figured out when it comes to software that’s really complex and needs lots of cycles of iteration to achieve the level of perfection you need to replace a human driver that we should leverage Silicon Valley talent and the people at Cruise to do some of that work.”

Vogt said Cruise could have stayed independent and avoided the initial culture clash with GM or any other company, for that matter. But in the end, staying independent was at conflict with the startup’s true mission, which is getting these self-driving cars out as quickly as possible.

“When we looked at what GM brought to table, which has decades of automotive experience, assembly plants, lots of capital—there’s no doubt we could accelerate that mission and compress the timeline by partnering with one of the biggest automakers in the world,” Vogt said. “We had to sort of suck up our pride and do what was right for the mission here.”