Before you read any further, let’s try something.

Take a few seconds and explain, in actual detail, how a zipper works. What is the mechanism that connects the teeth? What about the geometry of the teeth? What is the slider actually doing as it moves up and down and why can’t you just pull the zipper apart?

It’s a little more complicated than you’d think at first.

This has nothing to do with intelligence, it’s just that you’ve seen zippers your whole life and never really studied how they work.

Turns out this is true for almost everything.

In 2002, two Yale psychologists named Leonid Rozenblit and Frank Keil ran a now-famous study. They asked participants to rate, on a scale of 1 to 7, how well they understood how common objects worked. Things like zippers, toilets, bicycles, combination locks, crossbows, car speedometers, and piano keys.

Most people rated themselves as having a solid understanding. Confident. Somewhere around a 5 or 6.

Then the researchers asked them to actually explain how the objects worked. In writing, in detail.

After trying to explain what they thought they understood, participants re-rated themselves dramatically lower. They hadn't learned or forgotten anything, they had simply discovered the gap between feeling like they knew and actually knowing.

Rozenblit and Keil named it the Illusion of Explanatory Depth.

The illusion exists because we confuse familiarity with understanding. You see zippers every day. You use them without thinking. That repeated exposure feels like knowledge, because your brain has no incentive to distinguish between I can use this and I understand this.

It's an evolutionary shortcut. You don't need to understand the biochemistry of fire to cook with it. You don't need to understand the internal combustion engine to drive a car. Cognitive efficiency favors the illusion.

The problem is we apply the same thought process to things that actually matter.

Follow-up research pushed the idea into belief systems. People were asked to explain mechanistically, step by step, how specific ideas they supported or opposed would actually work. Not if they agreed with them, but how they would function.

When forced to explain, people's confidence in their positions dropped, just like in Rozenblit and Keil’s study. Many reported genuinely rethinking opinions they had held strongly for years.

It turns out the fix is just to explain what you think you know.

Say it out loud, write it down, or talk about it with someone else. See if you can come up with enough detail that you could convince a skeptic or teach someone who has never seen it before.

When you try this, you hit the edges of your knowledge almost immediately, and you can actually see where there’s missing information. This is the same mechanism behind the Feynman Technique, Socratic dialogue, and most serious teaching methods in history. Explaining forces compression. Compression reveals gaps.

It works for zippers. It works for your job. It works for your opinions.

And it's the fastest diagnostic tool you own for figuring out what you actually know versus what you merely recognize.

Prompt: A handcrafted stop-motion claymation scene strongly inspired by the gothic whimsy of Tim Burton, blended with the Victorian illustrative influence of Edward Gorey, featuring an intentionally random, dreamlike gothic background—mismatched pointed archways, uneven staircases that lead nowhere, oddly placed doors, crooked picture frames, scattered candles, tilted towers, and asymmetrical architectural elements that feel surreal yet carefully handmade. Everything should appear physically constructed rather than digitally rendered, with imperfect sculpted clay, visible fingerprints, soft dents, uneven edges, layered paint, and miniature set textures. Use a rich but restrained storybook palette of deep plum, midnight blue, moss green, antique gold, and desaturated teal, lit with moody practical-style lighting that resembles a real stop-motion stage. Center an eccentric character with elongated limbs, a slender silhouette, oversized expressive eyes, and theatrical posture, embracing charming physical imperfections. The tone should feel whimsical, slightly melancholic, and playfully macabre rather than frightening. The central focus is a truly unique, centipede-hybrid gothic gentleman wearing a monocle and waistcoat, gazing into an ornate cradle containing a swirling, tactile spiral galaxy. Format: 16:9, ultra-high detail, shallow depth of field, cinematic miniature realism, full bleed.

Got a second? Give some feedback on today’s article so we can keep making improvements to The Manifold.

PS—By the way, the zipper slider is a tiny wedge that forces the teeth together on the way up and pries them apart on the way down.