The problem is that they can't refuse to cooperate if each one fears that no one will join him. In a public demonstration, each protester can see the other protesters see the other protesters, and this common knowledge allows them to coordinate their resistance

Steven Pinker, ~5:00

Now, of course, it's only so long that an asset can levitate in midair, suspended by nothing but common expectation. Bubbles pop when the market runs out of greater fools who don't want to miss out on the next best thing or when the doubt itself becomes common knowledge. This can send investors running for the exits, each desperate to sell a security out of fear that everyone is desperate to sell it. The result can be a bank run or hyperinflation or a Great Depression.

Steven Pinker, ~ 7:20

That is why, in everyday conversation, we often don't blurt out what we mean in so many words, but veil our intentions in innuendo and euphemism, counting on our listeners to catch our drift.

Steven Pinker, 9:46

The point of innuendo is not plausible deniability because these euphemisms don't pass the giggle test, but rather deniability of common knowledge.

Steven Pinker, 10:44

And that's what lies behind the intuition that with bare-faced speech, you can't take it back. It's out there.

Steven Pinker, 11:39

Our relationships are underpinned by a common understanding of limitless loyalty and generosity. Privately, we know they're fictions, but making these rude realities common knowledge would pollute the pool of common assumptions that allow us to get along.

Steven Pinker, 12:00