What defines a great company culture? I worked for two iconic companies and founders with nearly polar opposite cultures. Amazon was heads-down, secretive, forthright. Facebook was open, transparent, collaborative. Here's what I learned about culture working for Bezos and Zuck:

Culture implicitly sets expectations for behavior. Strong cultures are well-defined with sharp edges, and well-understood by everyone in the organization top to bottom. Strong founders with unapologetic personalities set the culture early and maintain it as the company scales.

When I joined Amzn in 1999, we had top-secret teams working on new products like Auctions, Toys and Electronics. Before a product launched, the only people in the know were those who needed to know. Everyone else was told to keep their heads down and focus on their own work.

When I joined the secret team working on Kindle, my job was to convince publishers to create digital books. They couldn't understand why we suddenly cared about ebooks when nobody at the time was reading them. I begged Jeff to let me share our plans for Kindle but he refused.

Jeff was taking a cue from Apple. Tim Cook once shared with me that Apple put a precise dollar value on the free press they received from big product announcements, which was undermined by leaks. Secretive cultures try to avoid leaks by locking down information.

There's nothing wrong with a heads-down culture where employees are told to focus on their own work. It provides guardrails, avoids distractions, sets a serious tone. And yet, there is a certain distrust in telling employees to mind their own business. The knife cuts both ways.

When I joined FB in 2006, I was shocked at how much Zuck shared with the company. I advised him to share less to avoid leaks. His response: "I'm building a company that I would want to work for if I hadn't started FB. And I would want to work at a place that shares openly."

FB's open culture mapped to Mark's personality and a generational shift in employee expectations. It also mapped to Facebook's products which were built on sharing. Open cultures assume employees are less likely to leak if they are trusted and empowered with confidential info.

Transparency allows for ideas to come from anywhere in the organization. Teams at FB prolifically collaborate, share feedback, communicate. But at its worst, this type of culture can devolve into entitlement, insubordination, ceaseless complaining. The knife cuts both ways.

Open vs closed is one dimension of a company culture. FB was also more egalitarian, Amzn more hierarchical. Both companies had a high tolerance for failure (compared to Apple for example). The important thing about culture is clarity & consistency, especially as a company scales.

When we developed company values in the early days at FB, Zuck didn't want a bunch of corporate dribble postered on the wall. I argued against "Move Fast and Break Things" but Mark chose it precisely because it was controversial, clearly signaled culture of velocity & iteration.

Amazon's most memorable value was "ruthlessly escalate." This removed any question about how decisions would be made. It encouraged a culture where people would debate strongly held ideas, knowing the solution to disagreements was to bump it up to the next level of management.

Culture is maintained through rituals. I once showed up for Zuck's Friday Q&A with only 3 other employees, and Mark proceeded to answer our questions for an hour. 15 years later he still religiously hosts Q&As with all topics on the table. This is FB's ritual of transparency.

Walmart's culture was defined by Sam Walton's relentless work ethic and frugality. He held his management meetings on Saturday and charged employees 5 cents for cream in their coffee. Walton died in 1992 but the company still holds Saturday meetings and charges extra for creamer.

They key to a strong culture is consistency from the top. The CEO's job is to make sure everyone on the management team is on the same page. If a senior leader wants to create their own unique culture for their part of the org, they can't be allowed to stay.

The partnership between Mark and Sheryl was forged by their mutual commitment to a unified culture across the company. There can be small differences based on the work to be done, but core values must be shared across product and business teams. There can only be one CEO.

There are many benefits to a strong culture: it makes interviewing easier, gives employees a sense of belonging, helps avoid politics, provides energy and zeal, cuts through a lot of BS. No culture is perfect, but great companies and founders are highly intentional about culture.