Users aren't fed every post by every one of their friends -- users would be overwhelmed with posts flying by so fast they couldn't keep up -- so it's no secret

Users aren't fed every post by every one of their friends -- users would be overwhelmed with posts flying by so fast they couldn't keep up -- so it's no secret FB tweaks its feed algorithm to keep users engaged. And experimenting with network effects is what social networks do. Every time you see a picture of someone you like it's like a little shot of dopamine goes off in your head. Facebook wants to optimize those dopamine shots to continually bump engagement and create an experience where everyone is habitually checking their feed every 10 mins. This type of behavior design/economics research is done by Dan Ariely at MIT ("Predictably Irrational" http://www.ted.com/talks/dan_ariely_asks_are_we_in_control_of_our_own_decisions.html http://www.ted.com/talks/dan_ariely_asks_are_we_in_control_o...) and the Stanford Persuasive Tech Lab (http://captology.stanford.edu/ http://captology.stanford.edu/).