There are two phrases that have reliably marked every great financial bubble in modern history.
The first is “this time is different” — what Sir John Templeton called “among the four most costly words in the annals of investing,” the signal that investors have begun rationalizing sky-high valuations by convincing themselves that old metrics no longer apply. Carmen Reinhart and Kenneth Rogoff gave the phrase its academic weight in their landmark 2009 book This Time Is Different: Eight Centuries of Financial Folly, documenting how governments and investors had repeatedly convinced themselves that past crises wouldn’t recur — and were always proven wrong.
