Mosseri has enjoyed a rapid rise at the social media giant since since joining Facebook in 2008, and although the pair clearly get on now, the product designer turned head of Instagram revealed that their relationship wasn’t always smooth sailing.

“We argued a lot in the early years,” Mosseri said. “I remember pushing back a lot on a number of random unimportant design specifics.

“He was very results-focused and I cared about things I still care about now, but I didn’t care enough about other things. He was pushing me hard on the things I didn’t care about enough that I should have cared about.”

Looking back at his “26-year-old hotheaded self,” he added that defying what’s important to your boss is “probably not good career advice.”

But now, Mosseri insisted that he has learned how to better balance what he holds dear at work with whatever’s at the top of Zuckerberg’s priority list. 

“Mark is very consistent,” Mosseri said on the podcast The Colin and Samir Show. “He is always going to hold a really, really high bar. He’s always going to push you really, really hard. He’s always going to have very high expectations.

“You can, when you’ve worked with anybody for long enough, start to anticipate what their feedback’s going to be, what they care about. 

“So as long as you make sure you embrace that in addition to embracing whatever you believe in and how you want to approach the role, you have to find that balance.

“With Mark, I have that balance most of the time.”

How Mosseri built his success

Before joining the tech world, Mosseri had the far less glamorous experience of washing dishes and waiting tables. 

He graduated from New York University in 2005 and worked as a product designer and UI engineer for the now defunct company TokBox for two years before getting his big break at Facebook.

In the 16 years since, he’s scaled the company’s ranks from the bottom to the top, and he credits being a jack of all trades and “reliable” for his success.

“I wasn’t very good, I just had a lot of range,” Mosseri said. “I’m decent at a strangely large number of things—and I think that has really helped me.”

He was made head of Instagram following the resignation of the app’s founders in 2018, six years after Zuckerberg bought it for $1 billion, and has been unofficially placed in charge of Meta’s new darling, Threads. 

On his transition from product design to management, he continued: “Being more of a generalist is more advantageous.

“Being an executive is a very generalist type of role, so my career really accelerated when I leaned into that and was honest about what I wasn’t good at.”

Fortune reached Meta for comment.

The lesson: Work on what your boss cares about

Meta’s CTO, Andrew “Boz” Bosworth, similarly worked his way up the ranks. 

Having started out as one of Facebook’s first engineers before being plucked out for promotion after promotion, Bosworth said the difference between him and his peers wasn’t simply who could work the hardest. 

In an interview on Lenny’s Podcast, Bosworth revealed that he worked 120 hours a week and didn’t sleep more than four hours consecutively a day for two years.

“There are other people who do the exact same thing, maybe they worked harder, maybe they were smarter, maybe they did better,” he cautioned. “And it didn’t play out for them and it’s a big sacrifice.”

Instead, like Mosseri, he credits his success with putting himself forward for projects that are important to his boss and a result ending up under the “Eye of Sauron”—otherwise known as Zuckerberg’s beady watch. 

“If it’s the most important thing, you’re going to get a smaller piece. Everyone wants to be there,” Bosworth advised. “Get the piece that you can crush, kill, do a great job at, and grow from.”

The Facebook veteran also recommended volunteering to help out in an area that the company isn’t paying a lot of attention to, but is still really important to the business.

“As an executive, when there’s a huge dam holding up the floodwaters, you respect the heck out of that person who is holding that dam up.”