Millions of small investors have piled into India’s stock market in recent years, eager to build wealth by betting on the country’s economic growth. Catchy advertising and easy-to-open online trading accounts have wooed young people and retirees alike, demystifying investing and fueling the exuberance.

This week, many of those investors got a rude shock — and an introduction to the pitfalls of globalization — when Indian markets buckled from fears that President Trump’s new tariff regime would induce a global recession.

On Monday, the Indian stock market lost around $170 billion in value as its two biggest indexes plummeted, mirroring global markets that have swung wildly as investors game out the likelihood of a downturn. By Tuesday, the domestic market had rebounded, and many analysts were sanguine about India’s economic advantages in trade negotiations with the United States.

On Wednesday, though, India’s Sensex and Nifty 50 indexes were down again as a 27 percent tariff on Indian exports to the United States took effect. India’s central bank cut interest rates and reduced its growth forecast, citing the rapidly changing global landscape.

“The recent trade tariff-related measures have exacerbated uncertainties, clouding the economic outlook across regions, posing new headwinds for global growth and inflation,” Sanjay Malhotra, the governor of the Reserve Bank of India, said in a speech.

Many everyday investors, especially first-timers, were lurching between confusion and terror, unsure whether to blame their trading strategies or Mr. Trump.