Part of "move fast and break things" is a willingness to take big risks. The walls here at Facebook are lined with posters that say things like "What would you do if you weren't afraid?". Far from this being a meaningless platitude, Facebook is constantly willing to make massive changes to their product and potentially alienate users. It's quite a contrast to companies like Amazon and Microsoft which only experience change in a slow, evolutionary, and risk-adverse manner.
I think that it's really interesting that all companies that experience explosive growth, harp about their mantra to "keep the startup environment", but 99% of them fail, because they eventually give power to the <i>management</i> and not the engineers.