What made it possible was a culture of ownership.
And this wasn’t superficial. It wasn’t people trying to get political points on a performance review. It was literally: if you own something you take full responsibility for every aspect of it, no excuses, no blaming. No “I didn’t know about this.” No “the servers crashed, let me ask another team to fix it for me.” If you truly owned something, then no one at Facebook would say no—even if your idea was terrible, even if it didn’t work—because you were the person carrying the weight of the consequences.
This environment empowered very young engineers, straight out of college, to swing for the fences. It’s the same culture that let junior teams build React and GraphQL—not because a manager handed down a spec sheet, but because they saw a problem, owned it completely, and grew it because they had the authority to do so.