I would blame app designers, but I uninstalled all of them and ended up pissing away most of the day on HackerNews, so I think they're mostly blameless in my case.
You never know what you'll get when you reload (after some time has passed) (Random reinforcement.) Also, if you comment, you get random reinforcement in the form of (hopefully nice) replies and upvote points.
Ranking stories on the front page based on voting also is intended to draw an audience with similar interests.
Hacker news is addicting, but there is a noprocrast setting that only allows you on the site for maxvisit minutes at a time and doesn't let you back on until minaway minutes have expired. I just turned it on this week and it has changed my browsing habits immensely!
You never know what you'll get when you reload (after some time has passed) (Random reinforcement.) Also, if you comment, you get random reinforcement in the form of (hopefully nice) replies and upvote points.
Ranking stories on the front page based on voting also is intended to draw an audience with similar interests.