Stock market bubbles are fascinating stories.

Cryptocurrencies are the most recent speculative frenzy to erupt in spectacular fashion, with Crypto Winter joining a storied history that includes mania, the Roaring Twenties and the South Seas bubble. In his 19th century study of market madness – “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 consequences. “Men, as we have said, think in herds; we will see that they go mad in herds, while they regain their senses only slowly, and one by one,” he wrote.

Bubbles often emerge during periods of major innovation. The impact of these innovations on the economy is unpredictable, with the line between hype and new ways of doing business uncertain. Speculative enthusiasms test the implications of innovations. The same goes for long periods of regret when big bets dip in value. Booms and busts help investors and entrepreneurs determine whether or not innovations offer real promise for economic transformation.

Valuable insights 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 maybe the surviving crypto companies will signal the value of crypto. The price of collecting this knowledge is that many people influenced by crypto enthusiasts will lose money, sometimes huge sums.

There is a larger 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 struck me reading the deep dives of crypto journalists is how many crypto companies have offered owners double-digit returns to get them to deposit their crypto with them. Double-digit returns when bank savings rates were near zero and market rates weren’t much higher: those high returns screamed high risk.

A side story: Icelandic banks offered unusually high yields to attract global depositors in the early 2000s. Viking capitalists went on a buying spree overseas, but the country’s banking system imploded when the foreign money fled during the global financial crisis. The high yields offered by Icelandic banks were a signal that depositors’ money was under unsustainable threat. Always ask before you invest: is this promised return too good to be true? Giving a lucid answer to this question will save you money heartache.

Chris Farrell is Senior Economics Contributor, “Marketplace”; commentator, Minnesota Public Radio.