efeito
Zeigarnik effect
Uncompleted or interrupted tasks are remembered more easily than completed tasks.
Signal the end of each step; an open task keeps taking up space.
Kurt Lewin noticed in the 1920s that waiters remembered open orders in detail and forgot almost everything as soon as the bill was settled. Bluma Bliuma ZeigarnikMeasured, in 1927, that waiters remembered the orders still open better than those already delivered. The effect bears her name.One reference in this work:1927Über das Behalten von erledigten und unerledigten HandlungenSee on Wikipedia ↗See in the bibliography →, his student, took the observation into the laboratory and measured it. An interrupted task stays active in memory; a completed task is discarded. In interfaces, that explains why a half-filled progress bar bothers more than an empty screen, and why an “80% complete” profile pulls the person back. It is also why the same feature works so well for nagging: the tension that makes someone finish signing up is the same that makes someone unable to close the app.
Why there is no neuroscience here
The biological mechanism behind the effect, and how much of it was actually measured.
Here it is necessary to separate two findings that carry the same name, because the field tends to cite them as if they were one. The memory one — remembering interrupted tasks better — has an irregular replication record since the 1960s, and is not a safe basis for a design decision. What holds up better is the resumption effect, described by Maria Ovsiankina in the same laboratory: interrupted without closure, the person tends to return to the task spontaneously. That is the one that justifies this page’s recommendation, and neither of the two has an established neural mechanism.
The body this law presumes
Who it was measured on, and what changes when the body on the other side is another.
The effect says that a task begun and not finished keeps taking up space in the head, and that is what makes the progress bar work. SyrekFollowed 89 workers for five weeks and measured the other side of the Zeigarnik effect: a task left open on Friday spoils the weekend’s sleep.One reference in this work:2014Unfinished tasks foster rumination and impair sleeping: particularly if leaders have high…See in the bibliography → and Antoni followed 89 workers in a diary study over five weeks and measured the other side of that same lever: whoever ended the week with an open task ruminated more and slept worse at the weekend, and that weighed more on whoever worked under a management that demands high performance. The lever is the same, but what it does changes depending on who is on the other end. Nobody has measured this in people with anxiety disorders, and the bridge is mine. For whoever already ruminates on their own, the loop left open on purpose does not become motivation, it becomes the night spent awake.
How design translates it
What to do with it on a screen, without turning a finding into a rule.
How to measure this in your product
Leaving the person in a flow without signalling that the step is over keeps the tension lit. A “step 2 of 3” or a micro-feedback at the end of each step returns the closure that frees the head for the next step. The same retention serves engagement, and the criterion is this: the step counter reports progress and, at the same time, keeps the action open in memory, which helps whoever wants to finish and presses on whoever cannot stop.
Onde vira manipulação
The same lever, pointed at the person on the other side.
Automatically advancing the user from a fictional “Step 1: searching for courses” to a real “Step 2” leaves the task artificially unfinished. It works, and that is why the step is only justified when it actually exists on the other side.
Where it breaks
Where the law does not hold, holds less, or holds in reverse.
The other side of the effect is the cost. An open task is not just better remembered, it keeps taking up space, and the space is the same the person would use for something else. That is what Syrek and Antoni measured: a task left open on Friday spoils weekend sleep. A progress bar that never closes keeps the task open in the person’s head after they have left the product.
Um caso
A real product where this showed up, with what happened and where to check it.
The card that already came with two stamps
In 2004 a car wash handed out three hundred loyalty cards at random. Half asked for ten stamps to earn a wash and came with two already stuck on. The other half asked for eight and came empty. The effort was identical, eight washes. In nine months, 34% of the cards that came with the two stamps were completed, against 19% of the empty ones, and those who received them came back on average 2.9 days sooner between one visit and the next. The authors call this endowed progress and rest the effect on Zeigarnik, cited right in the first of the paper’s two theoretical reasons. What I add is the framing: what holds up today is resumption, and not memory. A task presented as begun and incomplete is completed more than the same task presented from scratch. Your interface’s progress bar does not inherit this for free. A meta-analysis of 32 experiments with online questionnaires found that the constant progress bar does not reduce abandonment, and that, when there was an incentive to take part, it increased it. What retains is the task already begun, and the bar on its own does not do that work.
Experimente
A piece to check in your own body what the text has just claimed.
Which card would you rather complete?
Two loyalty cards from the same car wash. Choose the one you would take, without doing the maths. Then reveal what the two ask for.
Choose one of the two.
Both cards ask for eight washes. A looks ahead because it has already been started, and that is what the resumption effect describes: a task presented as started and incomplete gets completed more than the same task presented from scratch. At the car wash, 34% completed the card with two stamps, against 19% for the empty one. On a screen, the "2 of 4" plays that role when it is true.
Fontes
Enunciado citado de Zeigarnik, 1927.
- ZEIGARNIK, B. Über das Behalten von erledigten und unerledigten Handlungen. Psychologische Forschung, v. 9, p. 1-85, 1927. Source
Leitura complementar: Zeigarnik Effect Laws of UX em inglês