What you tolerate is what you are. So, if you tolerate white supremacists on your platform, you're a platform for white supremacists ... Unless you say what is and is not acceptable on your platform, it just becomes a disaster because you want to be part of a community that share your values, and you don't share values with white supremacists.

Bill Gross at Idelab did this research where he looked at all of the different companies (200-300 companies) that he had invested in over his career and tried to figure out what it was that made them successful. Was it execution? Was it the market? Was it their financing? Was it their team? What was it? And it turned out that it was their timing, and that they had found a parade and gotten in front of it. They had found larger societal and cultural movements that were happening.

This is what I mean by creating a hospitable climate for certain types of behavior. Every founder of an online community must grapple with it daily. If you're not grappling with it, you're living with a false sense of neutrality. You're actually allowing your most extreme users to make the decision for you because, in these cases, a non-decision is also a decision.

Culture sticks. It's hard to appreciate just how much it sticks. The tone you set from day one, from the first greeting, is the tone you keep.

Every founder of an online community has to shape the culture from day one because the tone you set is the tone you're going to keep.

Whatever you are when you're [a small company] gets amplified when you're big, so take a really close look at what you are—the good and the bad.

Flickr was tested very early and very vocally by its users, and this shaped Caterina's fundamental approach to online communities: You have to know who you are, who you're for, and what you stand for.