Contrary to widespread expectations, commodity prices have not inexorably climbed. Economic growth has disappointed.
In 2012, Brazil's GDP grew only 0.9 percent, down from 2.7 percent in 2011 and 7.5 percent in 2010. The China story is similar: Growth has slowed, policies seem less sound.
Global investors' reappraisal was apparently triggered by the possibility that the Federal Reserve would reduce its $85 billion of monthly bond purchases. This would mean less money to prop up stock prices around the world, including in emerging markets.
Brazilian officials and some others complain that Fed policy whipsaws them: first, an inrush of money fosters easy credit and higher stock prices; then, an exit of funds does the opposite.
Fed actions inevitably cause investors to re-evaluate their portfolios, says Ubide. He also rates Turkey and South Africa as vulnerable to shifting investor sentiment.
Still, Ubide and many economists doubt a doomsday outcome. "There is no serious risk of a major global crisis," says Subramanian.
That could happen if uncontrolled sell-offs around that world exhausted countries' foreign- exchange reserves (mostly dollars) that ultimately enable them to import. Global trade and production would plummet.
By contrast, says Subramanian, today's market turmoil reflects an unavoidable adjustment to more normal Fed policy.
In a report to clients, Capital Economics, a consulting firm, says emerging-market countries have defenses against a broader crisis: high foreign-exchange reserves; low foreigncurrency debts; more flexible currencies.
All this sounds reassuring - and probably is. But nagging doubts remain.
Every major financial crisis of the past 20 years has begun with some relatively minor event whose significance seemed isolated: weakness of the Thai baht in the summer of 1997; trouble in the market for "subprime" U.S. mortgages in 2007; Greece's misreporting of its budget deficit in 2009.
Could this be "deja vu all over again"?