Facebook's biggest competitor is "not Facebook". There's tons of "not Facebook" that can hurt Facebook. Even other Facebook properties like Instagram and WhatsA

Facebook's biggest competitor is "not Facebook". There's tons of "not Facebook" that can hurt Facebook. Even other Facebook properties like Instagram and WhatsApp are "not Facebook" in the sense that they don't generate the same value of data that Facebook generates. "Not Facebook" includes other social media like reddit and Twitter and Youtube and LinkedIn etc, but also news sources like New York Times and BBC and Washington Post etc, and other OpenID login providers like Google and Github etc, and other messaging services like iMessage and Slack etc, and other sources of business information like Yelp and TripAdvisor and Foursquare etc. Every time you visit one of these "not Facebook" sites, Facebook loses. So Facebook reminds you that Facebook exists so you'll check Facebook first and might as well log into that site and app with Facebook and as long as you're here why not message your friends, oh by the way did you see this cool business near you and there's an event you just have to go to.