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Market bubbles are fascinating stories.

Cryptocurrencies are the most recent speculative frenzy to go spectacularly bust, with Crypto Winter joining a legendary history that includes the mania, the Roaring 20s, and the South Sea Bubble. In his 19th century study of market crazes — "Extraordinary Popular Delusions and the Madness of Crowds"— Scottish poet and journalist Charles Mackey captured the essential rhythm of exuberant market manias and their sobering drawn out aftermath. "Men, it has been well said, think in herds; it will be seen that they go mad in herds, while they only recover their senses slowly, and one by one," he wrote.

Bubbles often emerge during periods of major innovations. The impact of such innovations on the economy is unpredictable with the line between hype and new ways of business uncertain. Speculative enthusiasms test the implications of innovations. So do the long periods of regret when big bets plunge in value. Booms and busts help investors and entrepreneurs figure out whether innovations offer a genuine promise of economic transformation — or not.

Valuable information will emerge from Crypto Winter. We'll have a better idea if cryptocurrencies are little more than an environmentally damaging high-tech Ponzi scheme; or perhaps the surviving crypto businesses will signal the value in crypto. The price of gathering that knowledge is that many individuals swayed by crypto enthusiasts will lose money, sometimes considerable sums.

There is a broader investment lesson to highlight in the crypto boom and bust. When it comes to financial markets (and probably life in general) if something is "too good to be true," it probably is. What has struck me reading the deep dives by crypto journalists is how many crypto companies offered owners double-digit yields to get them to deposit their crypto with them. Double-digit yields when bank savings rates were essentially zero and market rates not much higher: Those high yields shouted high risk.

A parallel story: Icelandic banks offered unusually high yields to attract global depositors in the early 2000s. Viking capitalists went on a foreign buying spree, but the country's banking system imploded when foreign money fled during the global financial crisis. The steep yields offered by Iceland's banks was a signal that depositor money was unsustainably at risk. Always ask before investing: Is this promised return too good to be true? Giving a clear-eyed answer to that question will save you from money heartbreak.

Chris Farrell is senior economics contributor, "Marketplace"; commentator, Minnesota Public Radio.