A new study suggests that people who spend time looking at the acquaintances enjoying life of facebook are sad with envy.
http://www.plosone.org/article/info%...l.pone.0069841
Conclusion from the above report
"The human need for social connection is well established, as are the benefits that people derive from such connections [30]–[34]. On the surface, Facebook provides an invaluable resource for fulfilling such needs by allowing people to instantly connect. Rather than enhancing well-being, as frequent interactions with supportive “offline†social networks powerfully do, the current findings demonstrate that interacting with Facebook may predict the opposite result for young adults—it may undermine it."
People naturally share happy moments on Facebook (and a lot more besides)
Do you get sad when using Facebook?