How Instagram does it
Instagram's main feed, Reels, Stories, and Explore are all built on infinite-scroll architecture: the bottom of the list does not exist. Meta's own engineering blog publishes the ranking formula directly — content is scored as Expected Value = W_click * P(click) + W_like * P(like) – W_see_less * P(see less) + etc., where each engagement signal is weighted and the model retrains hourly on new data. The system gets better at predicting what holds you longest with every additional interaction.
Aza Raskin, who invented infinite scroll in 2006 while building a prototype for an earlier product, has publicly regretted the design choice ever since. In a widely-cited 2018 BBC interview he described the mechanism as "taking behavioural cocaine and just sprinkling it all over your interface, and that's the thing that keeps you like coming back and back and back." The Center for Humane Technology — which Raskin co-founded with Tristan Harris — names infinite scroll as one of a family of "addictive design features" engineered to manipulate human psychology and keep users on the platform regardless of whether the time is good for them.
The architecture is no longer Meta-only. TikTok, YouTube Shorts, X/Twitter, Facebook News Feed, and surfaces that pre-dated infinite (LinkedIn, Reddit) have all moved to bottomless feeds. The consequence reaches where the US Surgeon General named it in his 2023 advisory: a youth mental-health concern, time displacement from real life, and a family of dark patterns that exists because the optimization target is time-on-platform.