HN fits the pattern of addictive behaviour. (Trigger -> Action -> Variable Reward).

You are triggered to come here when you’re bored. Your action is simple loading (or reloading) the page. The variable reward is that you get interesting content and discussions...but you never know what they will be.

Over time this pattern of behaviour becomes habitual. You probably open Hacker News at similar times of the day in similar situations.

This basic pattern applies to all social media products. It’s very well understood and a key part of modern software design.