ThinkstockThat notification number
One trick social networks use is a notification number, showing you the number of people at a glance who have mentioned or followed you.
Notification numbers appear on the app icon to draw you in, then on the top or bottom menu to draw you in further. They play the same psychological trick on you that clickbait headlines do — they tell you that there's information you really want to know, but they don't tell you enough to satisfy.
A headline could say: "Patti LaBelle's Pies Are Selling for $40.99 on eBay."
But the clickbait version is: "You Won't Believe How Much Patti LaBelle's Pies Are Selling for on eBay" — which, you'll notice is even longer.
Notification numbers work just like that. Seeing a red "3" on the Facebook notifications bar is like a clickbait headline: "You won't believe what three people have said about you." You've got to click or tap. It's compulsive. And over time, it becomes addictive.
The biggest tool in the social media addition toolbox is algorithmic filtering. Sites like Facebook, Google+ and, soon, Twitter, tweak their algorithms, then monitor the response of users to see if those tweaks kept them on the site longer or increased their engagement. We're all lab rats in a giant, global experiment.
The use of algorithms for making social streams increasingly addictive explains a lot. It explains why Facebook (which has been tweaking its addiction algorithm the longest) now gets more than a billion users a day. It explains why Google never let you turn off algorithmic stream filtering all the way. And it explains why Twitter wants to algorithmically filter feeds, despite the general objection of users.
The tweaking of algorithmic filters for addiction means that in theory social sites get more addictive every day, and that the sites are in a war for survival where only the most addictive sites will survive. Meanwhile, our innate human ability to resist this addiction doesn't evolve.