Bitcoin once threatened to displace the dollar; now numerous competitors purport to do the same. Tesla Inc. was once about the only stock you could buy to bet on electric vehicles; now there is China's NIO Inc., Nikola Corp., and Fisker Inc., not to mention established manufacturers such as Volkswagen AG and General Motors Co. that are rolling out ever more electric models.

But for assets across the board to fall would likely involve some sort of macroeconomic event, such as a recession, financial crisis, or inflation.

The Fed report this past week said the virus remains the biggest threat to the economy and thus the financial system. April's jobs disappointment was a reminder of how unsettled the economic outlook remains. Still, with the virus in retreat, a recession seems unlikely now. A financial crisis linked to some hidden fragility can't be ruled out. Still, banks have so much capital and mortgage underwriting is so tight that something similar to the 2007-09 financial crisis, which began with defaulting mortgages, seems remote. If junk bonds, cryptocoins or tech stocks are bought primarily with borrowed money, a plunge in their values could precipitate a wave of forced selling, bankruptcies and potentially a crisis. But that doesn't seem to have happened. The recent collapse of Archegos Capital Management from reversals on derivatives-based stock investments inflicted losses on its lenders. But it didn't threaten their survival or trigger contagion to similarly situated firms.

"Where's the second Archegos?" said Mr. Bianco. "There hasn't been one yet."

That leaves inflation. Fear of inflation is widespread now with shortages of semiconductors, lumber, and workers all putting upward pressure on prices and costs. Most forecasters, and the Fed, think those pressures will ease once the economy has reopened and normal spending patterns resume. Nonetheless, the difference between yields on regular and inflation-indexed bond yields suggest investors are expecting inflation in coming years to average about 2.5%. That is hardly a repeat of the 1970s, and compatible with the Fed's new goal of average 2% inflation over the long term. Nonetheless, it would be a clear break from the sub-2% range of the last decade.

Slightly higher inflation would result in the Fed setting short-term interest rates also slightly higher, which need not hurt stock valuations. More worrisome: Long-term bond yields, which are critical to stock values, might rise significantly more. Since the late 1990s, bond and stock prices have tended to move in opposite directions. That is because when inflation isn't a concern, economic shocks tend to drive both bond yields (which move in the opposite direction to prices) and stock prices down. Bonds thus act as an insurance policy against losses on stocks, for which investors are willing to accept lower yields. If inflation becomes a problem again, then bonds lose that insurance value and their yields will rise. In recent months that stock-bond correlation, in place for most of the last few decades, began to disappear, said Brian Sack, a former Fed economist who is now with hedge fund D.E. Shaw & Co. LP. He attributes that, in part, to inflation concerns.

The many years since inflation dominated the financial landscape have led investors to price assets as if inflation never will have that sway again. They may be right. But if the unprecedented combination of monetary and fiscal stimulus succeeds in jolting the economy out of the last decade's pattern, that complacency could prove quite costly.

Write to Greg Ip at greg.ip@wsj.com

(END) Dow Jones Newswires

05-08-21 0014ET