Ever walk into a room and just know that everyone there understands exactly why you’re annoyed, even if you haven't said a word? It’s a weird, collective vibe. There’s a massive body of information that sits in the background of our brains, stuff we assume everyone else has access to as well. We call this common knowledge. But when you really dig into what all the people know, you realize it’s actually a fragile, shifting mess of cultural expectations, biological hard-wiring, and the occasional outright lie we all just agreed to stop questioning.
Language is the best example. You don’t explain to a stranger what a "chair" is because you assume they know. That’s the baseline. But then it gets weirder. We assume everyone knows that you don't talk in a quiet elevator, or that you shouldn't eat someone else's lunch from the office fridge. These are the unwritten rules of the world.
The Illusion of Transparency and Why We Misunderstand Each Other
Here’s the thing: we often overestimate how much other people are actually tracking. Psychologists like Thomas Gilovich have spent years studying the "illusion of transparency." This is the tendency for people to overestimate how well their internal states are known by others. You think your nervousness is written all over your face. It isn't. You think everyone knows you’re lying about liking that casserole. They probably don't.
This creates a gap. We navigate the world thinking there is a massive pool of shared awareness—what all the people know—but really, we’re all just guessing based on our own internal monologues. It’s kinda terrifying when you think about it. We’re all walking around assuming a level of synchronization that simply does not exist in reality.
The problem starts with the "Curse of Knowledge." Once you know something, it becomes physically impossible to remember what it was like not to know it. This is why experts are often terrible teachers. They literally cannot fathom the state of mind of a beginner. They think their complex jargon is just part of the basic set of facts that everyone should possess.
Cultural Anchors: The Facts We Can’t Shake
While much of our shared knowledge is a mirage, there are absolute anchors. These are the things that, regardless of where you are, seem to be part of the collective human "operating system."
Gravity. Fire is hot. Water is wet.
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But then there are the cultural anchors. In the 21st century, the internet has flattened these. We’ve reached a point where a meme created in a bedroom in Jakarta can become part of the shared vocabulary of a teenager in Oslo within forty-eight hours. This is a new development in human history. Historically, what all the people know was limited by geography. You knew what your village knew. Now, we have a global village of shared references—mostly centered around pop culture, tech giants, and global crises.
Take the "S" thing. You know the one. That stylized, geometric 'S' everyone drew on their notebooks in middle school? Nobody knows where it came from. There’s no brand attached to it. It’s not a logo for a secret society. Yet, children across multiple continents have been drawing it for decades without being "taught" by a central authority. It’s a piece of universal folk knowledge that bypassed the traditional gates of education.
The Danger of "Common Sense"
We love to cite "common sense" as the ultimate authority. "It's just what people know!" we scream at the TV. But common sense is a moving target.
In the 1800s, common sense told people that miasma—bad air—caused cholera. Everyone "knew" it. Doctors knew it. The public knew it. It wasn't until John Snow (the physician, not the King in the North) mapped the Broad Street pump that the "knowledge" shifted to germs.
Today, we have similar blind spots. We rely on heuristics—mental shortcuts—to navigate a world that is too complex for our brains to handle. These shortcuts become the "facts" we all agree on because they’re easier than doing the research. For example, most people "know" that you lose 80% of your body heat through your head. Except, you don't. That was a flawed military study from the 1950s where the subjects were wearing survival suits but no hats. Of course they lost heat through their heads; it was the only part exposed!
We keep these myths alive because they provide a sense of order. If we can agree on a set of facts, the world feels safer. We feel like we belong to the group.
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The Social Glue of Shared Ignorance
Sometimes, what all the people know is actually a shared silence.
Sociologist Eviatar Zerubavel talks about "socially constructed silence." These are the things that everyone knows, but everyone knows they aren't supposed to talk about. The "elephant in the room." This is a powerful form of collective knowledge. It requires a high level of social intelligence to recognize what is known but unmentionable.
Breaking these silences is what drives social change. When a group of people collectively decides to start talking about the thing "everyone knows but nobody says," systems shift. We've seen this with various social movements over the last decade. The power isn't in the new information—often, the information was already there—the power is in the transition from private knowledge to public shared knowledge.
How Information Silos are Breaking the "Universal"
We’re entering a weird era. For the first time, we are losing the "all" in "what all the people know."
Algorithmic feeds mean that your "obvious truths" are completely invisible to your neighbor. You might know everything about a specific political scandal, thinking it’s the biggest story in the world, while the person next to you has literally never heard the names involved. Their algorithm has fed them a completely different set of "universal" facts.
This fragmentation is dangerous. It erodes the baseline of reality required for a functioning society. If we don't have a shared pool of knowledge, we can't have a conversation. We’re just shouting across a void.
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Practical Ways to Navigate Common Knowledge
Since "what everyone knows" is often a mix of outdated science, cultural myths, and algorithmic bias, how do you actually stay informed? You have to be an active curator of your own brain.
First, get comfortable with saying "I don't know." It sounds simple, but it's the hardest thing for most people to do. We feel a social pressure to possess the same knowledge as the group. Resist that.
Second, verify the "obvious." If a fact sounds too convenient or if everyone is repeating it with the exact same phrasing, it’s probably a "zombie fact"—something that died years ago but keeps walking around. Use resources like the Cochrane Library for health claims or Snopes for cultural myths. They aren't perfect, but they’re better than the guy on TikTok.
Third, talk to people outside your circle. This is the only way to see the edges of your own "universal" knowledge. You’ll find that things you thought were absolute truths are actually just local customs or niche interests.
Finally, recognize that human connection doesn't actually require us to know all the same things. It requires us to be curious about what the other person knows. Instead of assuming you share a mental map, start asking people to describe theirs. You’ll find the world is a lot bigger—and a lot more interesting—than the small set of facts we all agreed to pretend we understood.
The goal isn't to know everything "all the people" know. The goal is to understand why we think we know it in the first place. That’s where the real insight lives. Stop trusting the collective autopilot. Check the data, question the unwritten rules, and don't be afraid to be the one who asks the "obvious" question. Most of the time, everyone else was waiting for someone to ask it anyway.
Moving forward, try this: the next time you hear someone start a sentence with "Well, as everyone knows...", stop. Ask them how they know it. Not in a jerk way, but in a curious way. You’ll be surprised how often the "universal truth" starts to crumble under even the slightest bit of genuine inquiry. That’s not a bad thing. It’s how we actually start learning again.