This can set off cycles of exuberant recursive mentalizing, as investors desperately search for focal points, each one buying an investment not because of its inherent productive value but because they hope to unload it at a profit on future investors, greater fools.这会引发一种亢奋的递归心理博弈循环——投资者拼命寻找“焦点”，他们买入一种投资并不是因为它本身具有生产价值，而是希望将它高价转手卖给未来的投资者，也就是所谓的“更大的傻瓜”。

This can set everyone off in search of conspicuous focal points such as Super Bowl ads. Everyone knows that everyone watches the Super Bowl. In 2022, cryptocurrency exchanges ran high-concept ads in which they tried to gin up a common expectation of rising prices not by touting any of the advantages of cryptocurrency but by warning, "Don't be like Larry. Don't miss out."这会让所有人去寻找显眼的焦点，比如“超级碗”的广告。人人都知道人人会看超级碗。2022年，加密货币交易所投放了创意十足的广告，他们试图制造一种价格上涨的共同预期，不是通过宣传加密货币的优势，而是通过警告人们——“别像拉里那样错过机会。”

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.当然，一项资产只靠共同预期“悬在空中”的时间有限。当市场上再也没有愿意接盘、不想错过下一个机会的“更大的傻瓜”，或者当怀疑本身变成了公共知识时，泡沫就会破裂。

This can send investors running for the exits, each desperate to sell a security out of fear that everyone else is desperate to sell it. The result can be a bank run or hyperinflation or a Great Depression.这会导致投资者争相出逃——每个人都急着卖掉手中的证券，因为害怕其他人也急着卖。结果可能就是银行挤兑、恶性通货膨胀，甚至是大萧条。

When Franklin Delano Roosevelt said, "The only thing we have to fear is fear itself," it was not a feel-good bromide, but a theorem of common knowledge.当富兰克林·德拉诺·罗斯福说“我们唯一需要害怕的就是恐惧本身”时，这并不是一句鼓舞人心的鸡汤，而是“公共知识”定理的体现。

With investors constantly on the lookout for focal points, financial leaders have to be wordsmiths, mystics and occasionally, comedians. Alan Greenspan once said, "Since I've become a central banker, I've learned to mumble with great incoherence."在投资者不断寻找“焦点”的环境下，金融领袖必须既是语言大师，又是神秘主义者，有时甚至是喜剧演员。艾伦·格林斯潘曾说：“自从我成了央行行长，我就学会了用极度含糊的方式咕哝说话。”

"If I seem unduly clear to you, you must have misunderstood what I said."“如果我看起来说得过于清楚，那你一定是误解了我的意思。”

After Jimmy Carter told his inflation czar, Alfred Kahn, never to use the self-fulfilling word "depression," he said, "OK, but we're in danger of having the biggest banana in 45 years."当吉米·卡特告诉他的通胀主管阿尔弗雷德·卡恩，绝不能使用那个会自我应验的词——“经济萧条”——时，卡恩说：“好吧，但我们正面临45年来最大的香蕉危机。”

My own interest in common knowledge comes from its role in social relationships. A relationship is a coordination game. Two people are friends or lovers or allies, or dominant and subordinate or transaction partners because each one knows the other one knows that they are.我个人对“公共知识”的兴趣，源于它在社会关系中的作用。一段关系本质上是一场协调游戏。两个人之所以是朋友、恋人、盟友，或者是上下级、交易伙伴，是因为他们彼此知道对方知道他们的关系。

And this common knowledge can be cemented by a number of common knowledge generating signals. Like eye contact, where you're looking at the part of the person that's looking at the part of you that's looking at that part of them. Or blushing, where you feel the heat of the cheeks, reddening of your cheeks from the inside, knowing that other people can see it from the outside.这种“公共知识”可以通过多种能生成公共知识的信号来巩固。例如，眼神接触——你在看对方看着你的那个部位；又或者是脸红——你从内部感受到脸颊发热变红，同时知道别人从外部能看到这一点。