Open a question in someone's mind, give them just enough to feel the gap between what they know and what they want to know, and they will act to close it. The gap must be specific and closeable, and the payoff must justify the promise.
In 1994, Carnegie Mellon professor George Loewenstein published a paper that changed how we think about curiosity. His insight was that curiosity is not simply an appetite for new information — it is a response to a gap. Specifically, a gap between what we know and what we feel we should or want to know. The gap is uncomfortable. It creates an itch. And we are strongly motivated to scratch it.
The key mechanism is that the gap has to be sized correctly. Too large and it is not a gap — it is just ignorance, which we are comfortable with. We do not feel anxious about not knowing the plot of every novel ever written. We do feel compelled to know how a novel ends after we have read half of it. The curiosity gap only opens once we know enough to feel the incompleteness — and it only pulls hard when the missing piece feels close enough to reach.
This is why “You will not believe what happened next” works on anyone who is already reading an article but lands flat on someone who has not started it. Why progress indicators are motivating (you can see how close you are) but “you are 0% done” is not. Why email subject lines that hint at something specific get opened and vague ones do not. The gap has to be felt before it can be closed.
“Curiosity is a cognitive itch — and, like a physical itch, it demands scratching.”
— George Loewenstein, 1994
An email subject line has one job: create enough pull to get opened. Not inform — that is the email's job. Not sell — that is the CTA's job. Just get opened. The curiosity gap is the most reliable mechanism for doing this, but it only works when the gap is specific enough to feel real and when the email delivers on what the subject implied.
Below are two inboxes. The first uses generic, transactional subject lines. The second uses the same email types but opened with curiosity gaps. The underlying emails are identical. What changes is whether the subject line creates a reason to open.
All four subject lines are accurate and descriptive — but they open no gap. There is no reason to open them that you do not already have from the subject line alone.
Each subject line opens a gap: a mistake you might be making, a counterintuitive decision, a challenged belief, something you missed. The emails themselves are identical.
Notice what makes each subject line work. “The UX mistake 80% of designers make on day one” implies you might be in the 80% — which creates a gap between your current behaviour and the right one. “We removed the feature 40,000 users asked for” is a counterintuitive statement that demands resolution — why would you remove something people want? “Why every font pairing guide you have read is wrong” directly challenges an existing belief. Each one opens a gap by implying that what you currently know is incomplete or wrong.
The curiosity gap does not only work at the point of entry — it can be used throughout a piece of content to maintain engagement. The technique is to answer one question while opening the next, so the reader is always in a state of partial resolution. Each section closes a gap and opens a new one. The reader is always pulled forward by something they want to know.
Below are two versions of the same article introduction. The bad version is front-loaded — it answers its own question before the reader has had time to feel the gap. The good version opens the gap and holds it open, giving just enough to deepen the curiosity before the payoff arrives further into the article.
The most common mistake designers make is not testing with real users early enough in the process. Many designers spend too much time refining visual details before validating whether the core concept works for their audience.
To avoid this, schedule user testing sessions as early as possible — even with paper prototypes. Get feedback on the concept before investing time in high-fidelity execution.
There are also secondary mistakes designers commonly make, such as designing for themselves rather than their users, and ignoring accessibility requirements. Both can be addressed through a user-centred design process.
The answer arrives in the first sentence. There is no gap to close — once you know the answer, the article has nothing left to offer.
When we surveyed 300 working designers last year, we asked them to name the biggest mistake they made when they were starting out. The answers were remarkably consistent — not in what they named, but in what they did not name.
Almost nobody said what most design education teaches you to watch out for. Nobody mentioned design principles. Nobody mentioned software skills or tooling. The mistake they described was something earlier — something that happens before a single pixel is placed.
The mistake is so common that most of the designers we surveyed assumed everyone else was doing it too — which is part of why it persists.
Four paragraphs in and the gap is still open — but it has been deepened. We know the answer exists, that it is consistent, and that it is surprising.
The good version is doing something structurally deliberate: each paragraph answers a micro-question (“what did designers say?”) while immediately opening the next one (“but what did they not say?”). The reader is always one step behind the answer — which is exactly where you want them. The quote from the anonymous designer is particularly effective because it deepens the gap emotionally. The reader is wondering if they are the person who did not realise for three years.
The curiosity gap is useful anywhere you need to create pull — email subject lines, article headlines, onboarding copy, notification text, product descriptions, feature announcements. In each case the same structure applies: reveal that there is something to know, create the sense that not knowing it is a problem or a missed opportunity, and make the resolution feel reachable.
The limit is honest use. A gap that genuinely cannot be closed — a headline that promises something the content does not deliver — burns the reader's trust faster than almost any other mistake. The gap is a promise. Closing it well keeps the relationship. Failing to close it ends it.
Loewenstein, G. (1994). The psychology of curiosity: A review and reinterpretation. Psychological Bulletin, 116(1), 75–98. · Litman, J. A. (2005). Curiosity and the pleasures of learning. Cognition & Emotion, 19(6), 793–814. · Berger, J., & Milkman, K. L. (2012). What makes online content viral? Journal of Marketing Research, 49(2), 192–205.