A few years ago, everyone was clicking. Today, we’re all scrolling. Twitter, Pinterest, Facebook, and as of this week, Instagram and Medium - it seems everyone is getting on the infinite scroll bus. What is it about this magical design pattern that has so many consumer web companies using it?

Not too long ago, users were forced to reload pages to progress from one piece of content to the next. Web designers were advised against creating websites with information appearing “below the fold”, the portion of the page underneath what is displayed on the screen. As mobile phones and tablets gained wider adoption, it looked like the swipe might become standard fare. But that’s all changed now. Today, designers are dumping the click and flick and opting for the scroll for one simple reason – it works.

The Endless Search

The infinite scroll is interaction design’s answer to our penchant for endlessly searching for novelty. Certainly, there are technical reasons for the scroll’s increasing ubiquity. The rise of dynamic content, like a new comment entering the feed, necessitated a better solution than pagination built for static content. But to really understand why the scroll works so well requires a brief trip inside the mind and back in time.

Our brains evolved through the millennia into incredible prediction machines, designed to help us make sense of our environment. Our species benefited from our ability to make good decisions based on what we know is likely to happen in the future, thus, keeping us alive long enough to make babies and spread our genes.

To make correct predictions, the brain accesses memories, which allow us to deduce what’s coming next in an nearly instantaneous process of pattern recognition. The ability to learn is simply the conditioning of the brain to recognize cause and (blank).

You were expecting “effect” weren’t you? Of course you were. That’s because your brain has learned that these two words, “cause” and “effect”, tend to go together. 

It’s this conditioning that creates cognitive shortcuts and habits, allowing us to process tremendous amounts of information all at once. Our brains move known causal patterns to long-term storage so that our attention can be devoted to learning new things.

And nothing holds our attention better than the unknown. The things that captivate, engross, and entertain us, all have an element of surprise. Our brains can’t get enough of trying to predict what’s next and our dopamine system kicks into high-gear when we’re waiting to know if our team will make the field goal, how the dice will land, or how the movie plot ends. Like a loose slot machine, the infinite scroll gives users fast access to variable rewards.

Interestingly, our brain isn’t wired to seek pleasure alone. In fact, much of our motivation comes from alleviating the pain of desire. Dopamine levels spike when we’re just about to find reward and plummet after we receive it. To get us to do just about anything, evolution uses this chemical cascade to induce anticipation, motivation, and finally pain alleviation. Somehow we call this endless merry-go-round “fun.”

Once You Pop

Few other methods for displaying information produce the curiosity to see what’s next like the infinite scroll. Like coffee and chocolate, the infinite scroll pairs particularly well with another increasingly-used design pattern, the masonry grid layout made famous by Pinterest. Cliff Kuang, editor of Co.Design, wrote, “… the Pinterest-style grid forces the eye to zig-zag through content, slowing down your scrolling but packing more images onto the screen at any given point.”

The barrage of enticing content speeds users up, enticing them to scroll, while the grid slows them down, retaining their attention and moderating their thirst for more and more stimulation. The visual tension is mesmerizing and addictive. Don’t believe me? I dare you to go to the Pinterest homepage and not feel tempted to scroll just once. It’s like opening a can of digital Pringles.

To Mobile and Back

The infinite scroll has benefited both mobile and web interfaces as designers seize the opportunity to make consistent experiences across both versions of their products. Once users learn how to use a product, they form habits related to their expectations of how the service works. It is here that design becomes a competitive advantage as users find it difficult to switch to a competitor’s product because it “feels weird” even if its functionally works just as well. 

Recently, the tail wags the dog as the constraints of the mobile experience influence the design of websites accessed on large screens. Creating an interface optimized for mobile and porting these interface decisions to the web, makes good sense given the projections that mobile is becoming the primary way people access the Internet. While certainly not perfect for every scenario, its efficient use of the mobile screen, ability to load dynamic content, and addictive characteristics, means we’ll all be doing a lot more scrolling.

Editor’s Note: Nir Eyal writes about the intersection of psychology, technology, and business at NirAndFar.com. He is the author of the forthcoming book Hooked: How to Drive Engagement by Creating User Habits. Follow him on Twitter @nireyal.

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