Picture a newspaper. It has a last page. A book has a last page, and a bag of crisps has a bottom. Each of those is a stopping point: a moment where the thing itself says that is all, and the beam from the last lesson is handed back to its owner.
Reach the bottom→More loads→Reach the bottom→More loads
A designer named Aza Raskin is often credited with a web page, from 2006, that loads more as you reach the bottom, so the bottom never comes. People call it infinite scroll. The words just mean a page with no last page. He has said since that he regrets it. Many feeds use it.
Last pagethat is all
vsvs
A feedmore loads
What did the last page of a newspaper do that a feed does not?
It made the paper shorter, so there was less to read.
Not yet. Length is not the point. A feed can be short on a slow day and still have no end. What is missing is the moment that says stop.
Nothing. People stopped reading papers whenever they liked, too.
Not yet. They could, and the paper also stopped them. A feed keeps only the reader's own stop; the paper's stop is gone, and it was a second way to stop.
It handed attention back. The paper itself said that is all.
Right. A stopping point is a decision the thing makes for you. Without one, every stop is a decision you make yourself, against a page that is still moving.
Never comeslow
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Coin-fliphighest
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Always comeslow
There is a second part, and it is about the brain. Dopamine is a chemical made in the brain. It rises when the brain expects a reward, before the reward comes. In one set of experiments on monkeys, it rose most not when a reward was sure, but when it was a coin-flip: it might come, it might not.
Pull down
↓→
Signal rises
↓→
Maybe new
A refresh of a feed is a coin-flip. Pull down, and something new might be there, or might not. In 2009 another designer, Loren Brichter, made the pull-down-to-refresh gesture for a Twitter app called Tweetie. The pull is a lever, and the lever pays out sometimes. That is the pattern the brain's signal rises highest for.
Picture a lever that sometimes pays a coin. Move how often it paid, and watch how many pulls a person makes after it stops paying altogether. Made up to show a shape found in animals and in people.
Paid pulls, of 2020 made up
Pulls after the last pay5 made up
How often it paid: Every pull
It paid every pull. The first dry pull is news, and the hand stops after about five.
Paid pulls, of 2010 made up
Pulls after the last pay20 made up
How often it paid: Half the pulls
It paid half the time. A few dry pulls mean nothing yet; the hand tries about twenty more.
Paid pulls, of 202 made up
Pulls after the last pay60 made up
How often it paid: One pull in ten
It paid one pull in ten. A long dry run was always normal, so the hand keeps going: about sixty more.
Which lever keeps a hand pulling longest after it has stopped paying?
The one that paid one pull in ten.
Right. A rare pay means a long dry run was never a sign of anything. The hand cannot tell stopped from not yet, so it keeps pulling. A feed on a slow day is this lever.
They are the same. A pull is a pull.
Not yet. The frames differ by twelve times. How often a thing paid in the past decides how long a hand keeps trying after it stops.
The one that paid every pull.
Not yet. When every pull paid, the first dry pull is news: something changed. The hand stops fast. Sure rewards are the easiest to walk away from when they end.
Move the control.
No last page→Pays sometimes→Hand stays on
Put the two parts together. A page with no last page never hands attention back. A lever that pays only sometimes keeps the hand on it longest. A feed is both at once. None of this needs a weak person: it works on people a little, whoever they are, and the designer of the endless page regrets it.
Put in order what happens from one pull of a feed to the next.
Tap them in the order they happen, first to last. Each tap gets a number.
Pull→Expect→Maybe→No stop→Pull
Right. Pull, expect, maybe, no stop, pull. There is no step where the page hands attention back, so the only way out is a decision made against a page that is still moving.
Five done
↓→
Done for todaynothing more
A learning app adds a feature. When you finish today's five exercises, it shows a page that says done for today, and nothing more. Using this lesson, what has it added?
Nothing much. People can close an app whenever they like.
Not yet. They can, and that is the first way to stop. The page adds the second: the thing itself saying that is all. The lesson began with why that matters.
A stopping point: a moment where the thing itself hands attention back.
Right. Done for today is a last page. It makes the decision to stop for the user, the way a newspaper's back page did.
A reward, so people will come back more.
Not yet. A reward is something that pays. A page that says done pays nothing; it ends. The lever in this lesson is the opposite of this page.
Lesson complete
A feed has no last page and pays only sometimes, and both keep a hand on it.