I read something earlier today that really made sense to me -- not about FaceBook in particular, but about social media in general. This is my own summary:
Before social media was "a thing", people felt the need to "keep up with the Joneses", but it was different. The Joneses were people who lived down the street, and -- yeah -- they DID HAVE the nicest house, a beach house, and a sports car -- but YOU KNEW THEM PERSONALLY, and you were aware that they had some warts: You KNEW that they fought about money and their oldest kid had a drinking problem.
In contrast, today we "see" people's lives on the internet, and because they only show us slivers of those lives -- only the things that are going well for them -- it's easy for us to get the idea that their lives are perfect. Because we don't know these people personally, we can't see those warts. Yet we seem to THINK that we're seeing the whole picture.
To add fuel to the fire, we get this perfect sliver-glimpse into MANY people's lives -- this one's vacations, that one's fantastic job, the other one's perfect children -- and we get the idea that we're the only people living ordinary lives. We get the idea that ALL these people are living perfect lives, and we are mediocre in comparison.