Just a few days ago, the Mobile World Congress tech conference took place in Barcelona and almost every tech giant checked in. Including one of our favorite notoriously known from the movie ‘Social Networking” and well, ‘Facebook’, Mark Zukerberg, the CEO and the founder of the biggest social media platform to exist in modern time.

Over the past 11 years, Mark Zuckerberg has built a $200 billion company with more than 9,000 employees everywhere from Austin to Auckland, Washington D.C. to Warsaw. As of December 2014, Facebook sees almost 900 million daily users.

Most entrepreneurs eventually step down and hand their companies over to professional CEOs, often at the insistence of their investors.

Mark Zuckerberg, who didn’t have any executive experience, or any traditional work experience for that matter, decided to stay on as a CEO of Facebook, despite the critics calling him out on his leadership skills throughout the years.

At the tech conference Mark revealed his one cardinal rule for hiring employees. As mentioned above, with over 9,000 employees there has to be a general criteria, right? According to The Telegraph, here’s what he looks for in an employee.

“I will only hire someone to work directly for me if I would work for that person… It’s a pretty good test and I think this rule has served me well.”

The Facebook founder also gave tips on how to create a successful empire for other CEOs and potential new startups.  According to CNN, “The most important thing is to keep your team as small as possible, also to just have faith in yourself and trust yourself… When you’re young you hear that you don’t have the experience to do things, that there are people with more experience than you. I started Facebook when I was 19.”