Definition
The curiosity gap, a concept popularised by marketer and writer Jonah Berger, is the information gap between what someone knows and what they want to know. When a subject line hints at a payoff without revealing it, the reader opens the email to close the gap.
Curiosity is one of the most reliable open-rate levers in email. It exploits a basic human drive: unresolved questions demand resolution. Subject lines like "The one mistake costing you sales" or "Why your emails aren't converting" create a gap the reader must close. AI inboxes have made the curiosity gap more important — the gap must now survive a two-line AI summary to earn the open.
How to Create a Curiosity Gap
- Hint at the payoff without revealing it — "we found something in your account"
- Use open loops — raise a question the body resolves
- Be specific, not vague — "this one line added 20% to CTR" beats "great tip inside"
- Never frustrate — the body must deliver on the promise
How AI Inboxes Change the Game
AI summaries now reveal what used to be the mystery. If the summary answers the question, the curiosity gap collapses before the open. Keep the essential surprise out of the first two lines and inside the body.
Related Terms
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
AI Content Detection
AI content detection refers to the growing ability of email clients, spam filters and consumers to identify machine-generated email copy. It matters for deliverability, trust and engagement in an era of mass-produced AI marketing email.
AI Email Summary
An AI email summary is a short, machine-generated overview of an email's key points, shown by Gmail, Outlook and Apple Mail before a recipient opens the message. It is reshaping how email marketers think about subject lines, preview text and open rates.
AI-Generated Content in Email
AI-generated content in email is copy, images, code or subject lines produced by artificial intelligence tools to speed up campaign production and testing.
AI Inbox
An AI inbox is an email client that uses artificial intelligence to summarise, sort, prioritise and sometimes answer emails before the human recipient reads them. It is transforming email marketing metrics and copywriting.
Frequently Asked Questions
They create an information gap the brain is motivated to close. The drive to resolve uncertainty is strong enough to overcome inbox inertia — at least until AI summaries close the gap for the reader.
Yes, if the body doesn't deliver. Clickbait-style gaps that frustrate readers teach them to stop opening. The gap must always be resolved by genuinely valuable content.
Keep the surprising detail out of the first two lines and the preheader. If the AI summary reveals the answer, there's nothing left to open for.