Latest / The Email Marketing Podcast with Fexingo: Newsletters, Open Rates, and Subscriber Growth / How Email List Curiosity Gaps Drive Clicks
Transcript
- Lucas: So we've talked a lot on this show about subject lines — what drives opens, what feels spammy, how personalization helps. But there's a specific psychological tactic that's been showing up more and more in top-performing newsletters, and it's called the curiosity gap. Luna: Right — the idea that you tease just enough information to make someone want to click, but you don't give away the payoff. It's classic 'open loop' stuff. Lucas: Exactly. And it's not new — journalists have been doing it for decades with headlines like 'You Won't Believe What Happened Next.' But email marketers have refined it into something more subtle. A 2025 study from Litmus looked at over 2,000 email campaigns and found that those using a curiosity gap in the subject line or preview text saw a 42% lift in unique clicks compared to straightforward subject lines. Luna: 42% is huge. But I imagine there's a fine line between intriguing and frustrating — or even feeling like clickbait. Lucas: There absolutely is. And that's the core tension. The best curiosity gaps work because they promise a specific, valuable answer — not because they're vague. So instead of 'You'll never guess what happened,' a good curiosity gap might be 'I sold my startup for $0 — here's why I'm not bitter.' You know the outcome, but you don't know the reasoning. Luna: That's a classic from The Hustle, right? They used that exact subject line years ago. I remember clicking it. Lucas: Same. And it worked because the headline created a contradiction — selling for zero dollars isn't normally a win, so you want to understand the logic. The curiosity gap is essentially a knowledge gap. You know the 'what' but not the 'why.' Luna: So the trick is to make sure the gap is something the reader actually cares about. If you tease something trivial, they feel cheated. Lucas: Right. Morning Brew does this well. They'll have a subject line like 'This one chart explains the yield curve inversion.' If you're their target audience — business-savvy, curious — you immediately want to see that chart. It's a promise of a quick insight. Luna: And they deliver. That's the other rule — you have to close the loop in the email or the landing page. Otherwise you damage trust. Lucas: Exactly. The curiosity gap only works if you satisfy it. If the content doesn't live up to the tease, you train your audience to ignore your emails. So it's a high-risk, high-reward tactic. Luna: I want to dig into the psychology a bit. Why does a knowledge gap make us click? It's not just 'curiosity killed the cat' — there's actual neuroscience behind it. Lucas: Yeah, there's a well-known study by George Loewenstein from the 1990s that basically says curiosity is the feeling of deprivation that comes from an information gap. When we sense there's something we don't know that we could know, it creates a kind of discomfort — and we're motivated to close that gap to relieve it. Luna: So the subject line creates a small itch, and the click is the scratch. That makes sense. But in email, you're competing with hundreds of other messages. The gap has to be strong enough to stand out. Lucas: And specific enough that it doesn't feel generic. A subject line like 'We need to talk' might work for a personal email, but for a newsletter it just feels ominous or spammy. But 'Your 401k might be costing you $50,000 — here's how' — that's a specific gap tied to a real pain point. Luna: That's a great example. It also uses a number — $50,000 — which adds concreteness. Numbers in subject lines tend to increase clicks. Lucas: They do. And you can combine curiosity gaps with other tactics. For instance, you could use a curiosity gap in the preview text — the snippet that appears after the subject line in most email clients. So the subject line says something broad, and the preview text deepens the mystery. Luna: Give me an example of that working in practice. Lucas: Sure. Say the subject line is 'The biggest mistake we made in Q3.' That alone might get some opens. But if the preview text says 'It cost us $200,000 — and we almost did it again' — now the gap is bigger. You have a dollar amount, a near-repeat, and a story. That's very clickable. Luna: That's smart. It also hints at vulnerability, which builds trust. They're admitting a mistake. Lucas: Exactly. And that's part of why curiosity gaps work well for B2B newsletters. Business readers are often looking for actionable lessons from others' failures. The gap signals that the email contains a case study or a lesson learned. Luna: So how do you test whether a curiosity gap is working without risking your whole list? A/B testing seems essential here. Lucas: Absolutely. You can run a simple A/B test with two versions of the same email — one with a curiosity gap subject line, one with a straightforward benefit-driven subject line. Measure opens and clicks separately. A curiosity gap might get more opens but fewer clicks if the content doesn't match. So you need to track both. Luna: And you need enough sample size to be statistically significant. For a small list, that's harder. Lucas: Right. If you have fewer than a thousand subscribers, the results might be noisy. But if you have a list of 10,000 or more, you can get reliable data in a few days. You can even segment by engagement level — see if curiosity gaps work better for your most engaged subscribers or for lapsed ones. Luna: I'd guess they work better for engaged subscribers, because those people already trust you enough to click. A lapsed subscriber might see a curiosity gap as one more reason to hit 'unsubscribe.' Lucas: That's a really good point. And it ties back to the ethics of it. If you use curiosity gaps on a cold list or a list that hasn't opted in recently, you risk feeling manipulative. The gap should be a natural part of the value you're offering, not a trick. Luna: I think the line is: does the email deliver on the promise? If yes, it's a effective tactic. If no, it's clickbait. And subscribers can tell the difference. Lucas: 100%. And that's why the best newsletters — like Stratechery, like Milk Road, like The Hustle — they all use curiosity gaps but they also have incredibly high-quality content. The gap is just the packaging. Luna: Let's talk about the mechanics of writing a good curiosity gap subject line. What are the do's and don'ts? Lucas: First do: be specific. 'The one metric that predicts churn' is better than 'An important metric.' Second do: create a contrast or contradiction. 'Why our best quarter was also our worst' — that creates tension. Luna: Don'ts: don't be overly negative. 'Your business is failing and here's why' might get clicks, but it also annoys people. And don't make the gap too wide — if you say 'This email contains the secret to infinite revenue,' no one believes you. Lucas: Exactly. And one more do: use a question that implies a surprising answer. 'What do Amazon and your local bakery have in common?' That makes you think, and the answer is likely interesting. Luna: I've also seen curiosity gaps work in the sender name. Like when a person's name is used instead of a brand. 'From the desk of...' creates a gap about what that person wants to tell you. Lucas: Yes, that's a good one. Especially for solopreneurs or consultants. When the email comes from 'Alex at GrowthLab' rather than 'GrowthLab Newsletter,' it feels more personal and the curiosity gap is about the relationship. Luna: So what's the single biggest mistake you see marketers make with curiosity gaps? Lucas: Overusing them. If every email tries to create a gap, the reader becomes numb. The gap only works if it's novel. If you use it three times in a row, it feels like a formula. I'd recommend using it for your best, most interesting content — maybe once a week for a daily newsletter, or every other send for a weekly one. Luna: That makes sense. You want the gap to signal that this email is special. If everything is a gap, nothing is. Lucas: Precisely. And that's also why segmenting your list matters. You can test curiosity gaps on your most engaged segment first, see the reaction, and then roll it out more broadly. That way you minimize risk. Luna: I want to come back to the Litmus study. 42% lift in unique clicks — that's impressive. But was that across all industries, or specific verticals? Lucas: The study included B2B and B2C, and the effect was strongest in B2B — about 50% lift — and in media/publishing, about 45%. For e-commerce, it was lower, around 30%. Probably because e-commerce emails are more transactional — people are looking for discounts, not stories. Luna: Interesting. So the curiosity gap works best when the email contains information, not just a sale. That aligns with what we've been saying. Lucas: Yeah. And it's also more effective for newsletters than for promotional blasts. A weekly newsletter is expected to have interesting content, so the gap feels natural. A promotional email with a curiosity gap can feel like a bait and switch if the 'gap' leads to a product page. Luna: Right. That's a quick way to lose trust. So if you're in e-commerce, you're better off using curiosity gaps in your content emails — like blog post roundups or guides — rather than in your sales emails. Lucas: Exactly. And that's a good rule of thumb for anyone: use the curiosity gap when you have genuinely interesting content to share. Not when you're trying to push a metric. Luna: Alright, so let's say I'm a marketer listening and I want to try this. What's your recommended first step? Lucas: Pick one email this week — your best piece of content — and write three subject lines that use a curiosity gap. Then A/B test them against your usual subject line. Track both opens and clicks, and look at the click to open rate especially. That tells you if the gap led to genuine engagement. Luna: And if the click to open rate drops, it means the email didn't deliver on the promise. That's a red flag. Lucas: Exactly. You want the click to open rate to stay the same or improve. If opens go up but clicks go down, you're just tricking people into opening. That's bad for deliverability and trust. Luna: One thing I've noticed is that the curiosity gap works especially well when paired with a strong preview text — since that's often the second thing people see. If you can create a mini-curiosity gap in the preview text, it compounds the effect. Lucas: Yeah. And preview text is a bit of a dark horse. A lot of marketers don't optimize it. But it's prime real estate. I'd say treat it as a second subject line. Luna: Alright, I think we've covered the strategy pretty well. Before we wrap, I'm curious — do you have a favorite curiosity gap subject line from a newsletter you subscribe to? Lucas: I think the best one I've seen recently was from a fintech newsletter: 'The bank that lost $2 billion and nobody noticed.' I clicked immediately. It turned out to be a well-researched piece on accounting loopholes. The gap was perfect — a huge loss, but hidden. Luna: That's a good one. Mine was from a marketing blog: 'We tested 100 subject lines. This one won by 300%.' It's a meta example — using a curiosity gap about curiosity gaps. Lucas: Ha, that's great. And it's self-referential, which makes it even more intriguing. Listen, if this conversation has given you a new angle to test in your own email marketing, that's exactly what we hope for on this show. Luna: And if you've found these episodes useful, the way we keep this show ad-free and independent is through listener support. You can buy us a coffee at buy me a coffee dot com slash fexingo. That's buy me a coffee dot com slash fexingo. Lucas: Yeah, it genuinely helps us keep going — and keeps the content focused on what's useful for you, not for sponsors. So thank you if you've already supported, and if you haven't, no pressure. Luna: Alright, back to the topic. So the key takeaway from today: curiosity gaps are powerful, but they're a scalpel, not a sledgehammer. Use them sparingly, deliver on the promise, and always test. Lucas: And remember — the goal isn't just to get opens. It's to build a habit of clicking because readers know the content behind the gap is worth their time. That's the long game. Luna: Well said. Next week we'll dig into another email marketing lever — see you then.