Podcast Summary: Something You Should Know

Host: Mike Carruthers
Guests: Steven Pinker (Harvard Psychologist, author), Emily Labor Warren (Health and Science Reporter)
Date: September 22, 2025
Episode Theme:
Exploring the concept of common knowledge—how we know what “everyone knows,” why some social norms stick, how culture shapes our expectations, and why some people are always late (and how their “time personality” works).

Main Themes & Purpose

This episode delves into the concept of “common knowledge”—the things we all know everyone knows—and why it matters for social order, economics, and personal interactions. Harvard psychologist Steven Pinker explains the power and fragility of common knowledge in everything from money to manners. In the second half, Mike interviews journalist Emily Labor Warren on why some folks are chronically late, what “time personality” means, and how cultural differences shape our relationship to the clock.

Key Discussion Points

1. You Don't Know What You Really Look Like

[02:40] Short Insight by Mike Carruthers

• Research shows people often choose less accurate photos of themselves compared to strangers.
• Memory and desire to look flattering can distort self-image.
• Smiling photos tend to be judged as more accurate, despite official guidelines discouraging smiles in passport photos.

2. What is Common Knowledge? (with Steven Pinker)

Interview Start: [05:45]

Defining Common Knowledge

• Steven Pinker [06:12]:
  “Common knowledge refers to the case where I know something, you know it, I know that you know it, you know that I know it…ad infinitum. It's necessary for coordination, for two people being on the same page.”
• Example: Meeting someone without cellphones; both need a way to agree on a spot (“rendezvous problem”).
• Currency and traffic norms rely on everyone knowing that everyone knows the rule.

Everyday and Large-Scale Coordination

• Pinker gives the example of everyone accepting paper money because it’s common knowledge that others do too.
• Driving on the right: works only because we assume everyone else knows to do it; fragile if that belief breaks down.

Sweden’s Overnight Traffic Switch

[11:21]

• Sweden changed from driving on the left to right overnight (midnight on New Year's).
• The public, shared, “popped out” time made it common knowledge and avoided chaos.

Coordination Failures and “Popping Out” Solutions

[12:54]

• Psychological experiments show people gravitate toward obvious choices (e.g., meeting at the Grand Central clock, picking the number 1).
• Common knowledge helps solve the “rendezvous problem” and affects everything from investments to bank runs.

Notable Quote:

“A bank run is the opposite: I better get my money out of the bank because other people are taking their money out of the bank because they’re afraid that other people are taking their money out of the bank.”
—Steven Pinker [15:22]

Beauty Contests, Investment Bubbles, and Herd Mentality

[13:50]

• John Maynard Keynes’s “beauty contest” analogy: people don’t just pick what they think is best, but what they think others will pick.
• Investment bubbles and panics are often driven by what we collectively think everyone else is thinking.

How Does Knowledge Become Common Knowledge?

[22:25]

• Public, conspicuous announcement or occurrence creates common knowledge.
• Sometimes, society uses “hints and euphemisms” to avoid making something public, preserving plausible deniability.

“Once it is out there…everyone knows that everyone knows. That can change everything.”
—Steven Pinker [22:37]

Self-Fulfilling Prophecies: The Toilet Paper Shortage

[20:02]

• Panic buying during COVID was caused not by actual shortage but by the belief that others would panic buy.
• The Johnny Carson anecdote: Jokes about a shortage led people to believe (and thus create) a shortage.

“There wasn't any real shortage of toilet paper until people thought there might be a shortage…And that created the shortage.”
—Steven Pinker [20:06]

• Stores posting “limit 1” signs serve both as a logistical fix and as a reassurance mechanism—rebuilding common knowledge and confidence.

Is Common Knowledge Human Nature or Culture?

[25:25]

• Pinker argues this is a foundation of culture: shared knowledge, customs, and values.
• Norms are maintained because “everyone knows that everyone knows”—not law enforcement.

Facial Expressions & Blushing as Common Knowledge Generators

[26:25]

• Blushing is both a physical and social phenomenon: everyone knows you've breached a norm, and you know they know.
• Blushing signals, “I know I screwed up,” and is often regarded sympathetically.

“Blushing is endearing. That's right. Even though it's painful to be the blusher, it actually raises your standing. And other people think better of you when you blush.”
—Steven Pinker [28:18]

Wrap-Up

[29:03]

• The power of common knowledge is usually invisible, but it shapes everything from traffic to trust, money, etiquette, and emotions.

3. Why Are Some People Always Late? (with Emily Labor Warren)

Interview Start: [32:35]

Time Personality and Cultural Attitudes Toward Time

• Emily’s article explores “time personality”—monochronic (linear, on-time, task-by-task) vs. polychronic (flexible, multitasking, flow) approaches.
• Many cultures, including some in Latin America, Africa, and the Middle East, are polychronic. Northern US/Europe tends to be monochronic.

Notable Quote:

“Time is not the clock…We haven’t had clocks for very long in human history.”
—Emily Labor Warren [32:52]

• Punctuality is a relatively modern, industrial concept, driven by things like train schedules.
• Many cultures see value in “being present” over “being prompt.”

Social Conflicts Over Punctuality

• Monochronic individuals (often American or Northern European-leaning) see lateness as disrespectful: “If you said we’d meet at 9, it's an agreement.”
• Polychronic cultures value ongoing interactions more—leaving a conversation abruptly to keep another appointment can seem rude.

“If you cut off a conversation prematurely just because you have another appointment…in a certain culture, that feels tremendously rude.”
—Emily Labor Warren [37:08]

• Within every culture, there is individual variation.

Coping Strategies and Social Negotiation

• Both guests and host agree: real-world situations (catching planes, starting work, etc.) require punctuality.
• Leaving some flexibility—calling if running late, showing understanding in informal settings—can ease social tension.
• “Being late to a party is almost expected,” says Mike [42:54]. “Showing up on time can seem rude—unless you’re there to help.”

Polychronic vs. Monochronic Preferences

[45:49]

• The difference extends to multitasking: polychronic people are comfortable bouncing between tasks, while monochronic folks prefer to focus and complete one task at a time.
• Studies show performance differences: puzzle-solving is more effective when task structure matches a person’s time style.
• These are preferences, not hardwired traits—people can adapt based on context.

“These time styles are preferences. They're not traits…sometimes the best thing to do is…think about the context.”
—Emily Labor Warren [48:12]

Respect and Mutual Understanding

• The key takeaway: acknowledge that people are different, that punctuality isn’t the only value, and context (work/fun/social emergencies) should choose the approach.
• Recognizing these differences can help reduce frustration and improve relationships.

4. Quick Tips: How to Snap Out of a Bad Mood

[51:38] Quick segment by Mike

• Have some tea—provides an instant feel-good lift.
• Exercise while watching TV—double the mood boost vs. exercising without distraction.
• Reach out to friends—a quick chat can lift your spirits.
• Order takeout—sometimes making fewer decisions helps when you’re stressed.

Notable Quotes

| Quote | Speaker | Timestamp | |------------------------------------------------------------------------------------|-------------------------|-----------| | “Common knowledge refers to the case where I know something, you know it, I know that you know it, you know that I know it, [etc.]” | Steven Pinker | 06:12 | | “A bank run is the opposite: I better get my money out … because other people are taking their money out ...” | Steven Pinker | 15:22 | | “There wasn't any real shortage of toilet paper until people thought there might be a shortage ... and that created the shortage.” | Steven Pinker | 20:06 | | “Once it is out there…everyone knows that everyone knows. That can change everything.” | Steven Pinker | 22:37 | | “Blushing is endearing. That's right. Even though it's painful to be the blusher, it actually raises your standing.” | Steven Pinker | 28:18 | | “Time is not the clock…We haven’t had clocks for very long in human history.” | Emily Labor Warren | 32:52 | | “If you cut off a conversation prematurely…in a certain culture, that feels tremendously rude.” | Emily Labor Warren | 37:08 | | “These time styles are preferences. They're not traits… think about the context.” | Emily Labor Warren | 48:12 |

Important Segment Timestamps

• [02:40] — Why people can’t recognize their own current face in photos
• [05:45] — Steven Pinker introduces the concept of common knowledge
• [11:21] — Sweden’s traffic switch as a mass coordination problem solved
• [13:50] — Beauty contest and investment bubbles as common knowledge phenomena
• [20:02] — Toilet paper panic-buying during COVID
• [22:25] — How common knowledge forms (public information, euphemisms)
• [26:25] — Blushing and social signals as “common knowledge generators”
• [32:35] — Emily Labor Warren on time personality and cultural variation in punctuality
• [45:49] — Polychronic vs. monochronic approaches and implications for multitasking
• [51:38] — Tips for instantly improving a bad mood

Memorable Moments & Takeaways

• Common knowledge isn’t just what most people know—it’s what everyone knows that everyone knows. This recursive awareness is vital for everything from traffic safety to financial markets.
• Social norms and even panics can arise “out of nothing,” proving that common knowledge has real, material consequences—a joke can cause a shortage if enough people take it seriously.
• Being late or punctual is not simply a matter of manners, but a deeply cultural—and even neurological—issue. Recognizing differences in how people experience time can improve relationships and reduce needless stress.
• In the end, context and compassion matter: adapt your 'time personality' as needed, and remember, sometimes it’s the small, shared rituals and expectations that keep society running smoothly.

For further reading:

• Steven Pinker’s book: When Everyone Knows That Everyone Knows
• Emily Labor Warren’s article: “Always Late? Blame Your Time Personality” (NYT — see show notes for link)