Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How a Single Underline Lifted Response by 423 Percent
Transcript
- Lucas: So picture this: it's the mid-1980s, a nonprofit organization is testing two versions of a fundraising letter. Same copy, same layout, same envelope. The only difference is one word in the opening paragraph is underlined in one version and left plain in the other. Luna: And I'm guessing the underline won by a lot, given this is a copywriting podcast. Lucas: A lot is an understatement. The underlined version pulled a response rate that was four hundred and twenty-three percent higher. Not twenty-three percent. Four hundred and twenty-three. That's not a typo. Luna: Wait, so one underlined word nearly quintupled donations? That's wild. Which word was it? Lucas: The word was 'you.' The sentence read something like, 'We need your help to save the children.' The 'your' was the underlined word in the winning version. Luna: Okay, that makes a kind of sense. 'You' is already a powerful word in copywriting. Underlining it is like shouting it in print. Lucas: Exactly. And that's the thing — the test wasn't about the word itself, it was about the visual emphasis. The underline acts as a visual cue that says 'pay attention here.' It exploits what psychologists call the pop-out effect. Luna: Before we dig deeper, I want to mention something. This is exactly the kind of concrete, actionable insight that makes this show valuable, and we deliberately keep it ad-free. If you find these episodes useful and want to support that choice, the link is buy me a coffee dot com slash fexingo. No pressure, just a way to keep the podcast independent. Lucas: Yeah, it's a small way to help us keep doing deep dives like this one. Back to the underline test — the pop-out effect is a well-documented phenomenon in visual perception. When a single feature like an underline is distinct from its surroundings, it automatically grabs attention. The reader's eye is drawn to it before they even consciously register the content. Luna: So the underline bypasses the logical brain and goes straight to the primitive attention system. Lucas: Exactly. And in a fundraising letter, that's gold. Because donors skim. They don't read every word. Underlining 'you' makes the reader feel personally addressed even if they're just scanning. That personalization triggers a sense of obligation. Luna: But wait — what if you overuse it? Underline every other word and the effect would wear off, right? Lucas: Right. The key is scarcity. In the winning version, only that one word was underlined. The control had no underlines at all. The test proves that a single, strategic underline can be incredibly powerful. But if you underline everything, nothing stands out. Luna: So it's the same principle as bold or italics. Why underline specifically? Why not bold or all caps? Lucas: Great question. Underline has a unique history in typewritten documents. Before word processors, underlining was the only way to emphasize text. So it carries a subconscious association with importance, with official documents, even with hyperlinks in the digital age. But the real reason it worked so well in that test is that it was unexpected. In a sea of plain text, one underlined word is a visual anomaly. Luna: And anomalies get noticed. So for modern marketers, does this translate to email subject lines or landing page headlines? Lucas: Absolutely. For email, you can't underline in the subject line — most email clients strip formatting. But you can use the same principle with brackets, parentheses, or emojis. One standout character among letters. One test I read about used a single pair of brackets around a key word in the subject line and lifted open rates by twenty-two percent. Luna: So the tactic is really 'choose one element to visually differentiate, and make it count.' Lucas: Yes. And it doesn't have to be underline. It could be a different color, a larger font size, or even a hand-drawn arrow. The principle is the same: create a visual anchor that breaks the pattern. The brain loves patterns, but it also loves pattern interruption. Luna: I've seen this work in web copy too. On a landing page, if you highlight one benefit in bold or a different color, it can increase conversion. But a lot of marketers go overboard and highlight everything. Lucas: That's the biggest mistake. I've audited countless landing pages where the entire headline is bold, plus the subhead, plus three bullet points. That's not emphasis — that's visual noise. The 423 percent lift came from restraint. One word. Luna: So how do you decide which word to underline? Is it always 'you'? Lucas: Not always. In fundraising, 'you' is a safe bet because it centers the donor. But in e-commerce, it might be the product name or a benefit word like 'free' or 'guaranteed.' The key is to underline the word that carries the most emotional weight. The word that, if the reader only saw that one word, they'd still get the gist of the offer. Luna: Test it, basically. Don't assume. Lucas: Always test. The original test was a simple A/B split. And the results were so dramatic that the nonprofit probably ran it again just to make sure it wasn't a fluke. I have a feeling it held up. Luna: Let's talk about the psychological mechanism a bit more. You mentioned the pop-out effect. Is there a specific term for why underlining works in a persuasive context? Lucas: There's a concept called the 'von Restorff effect,' also known as the isolation effect. It says that an item that stands out from its peers is more likely to be remembered. In a list of words, the one that is different — say, underlined — is recalled more often. That's exactly what's happening here. Luna: So the reader is more likely to remember that 'you' was underlined, and therefore more likely to feel personally addressed when they think back on the letter. Lucas: Exactly. And memory drives action. If they remember the letter as being about them, they're more likely to donate. It's a subtle cognitive nudge, but with a four hundred percent lift, it's anything but subtle in outcome. Luna: Are there any downsides to underlining? Like, could it seem desperate or gimmicky? Lucas: It could, if overdone or used in the wrong context. For a high-end luxury brand, underlining might feel tacky. But for a nonprofit asking for donations, it's appropriate. Context matters. Also, in digital copy, underlined text is often perceived as a hyperlink, which can confuse readers if it's not actually clickable. Luna: Right, so you have to be careful with web copy. Maybe bold or a different color is better online, but underline still works in print. Lucas: Precisely. That's why the original test is so instructive: it was a print letter. In that medium, underline had no competing associations. Today, we have to adapt the principle to the medium. Luna: So if I'm writing a direct mail piece today, should I underline one word? Lucas: I would test it. But I'd also test underlining a phrase like 'you personally' or 'your help.' The original test used one word, but a short phrase might work too. The key is to isolate the variable and measure. Luna: What about the P.S. in a fundraising letter? A lot of copywriters say the P.S. is the most read part. Should you underline there? Lucas: Absolutely. In fact, many classic direct mail letters underline key words in the P.S. because it's often the last thing the reader sees. Underlining 'today' or 'now' can create urgency. But again, just one word. Luna: I'm thinking about the broader lesson here. It's not really about underlining. It's about the power of deliberate visual hierarchy. One intentional break in the pattern can have an outsized effect. Lucas: That's exactly the takeaway. The underline is just a tool. The principle is: decide what matters most, then make it visually distinct. Everything else should recede. Most copy tries to shout everything, and as a result, nothing is heard. Luna: So three tips from this episode: one, choose one element to emphasize. Two, make sure it's the most emotionally charged word or phrase. Three, test it against a version with no emphasis. Lucas: Perfect summary. And if you run that test, I'd love to hear the results. Send us a note on social media. We're @Fexingo on most platforms. Luna: Until next time, keep your copy sharp and your underlines rare. Lucas: See you next episode.