It was a good year for investors who weathered historic swings in the market. The year 2025 was scary good for investors.It was scary because the U.S. stock market plunged to several historic drops on worries about everything from President Donald Trump’s tariffs to interest rates to a possible bubble in artificial-intelligence technology. In the end, though, it was a good year for anyone with the stomach to stick through the swings.S&P 500 index funds, which sit at the heart of many savers’ 401(k) accounts, returned nearly 18% in 2025 and set a record high on Dec. 24. It was their third straight year of big returns.Here’s a look at some of the surprises that shaped financial markets along the way: