During the fourth quarter of 2018, the business news was dominated by global trade wars, geopolitical tensions, the partial shutdown of the U.S. government, central-bank policies and interest rates. At the same time, investors worried about the impact that slowing global economic growth would have on individual companies.

Previously, as major U.S. equity indexes had surged toward all-time highs during the spring and summer of 2018, a relatively small number of technology and internet-related stocks had led the way. The most-popular of these were the so-called FAANG stocks—Facebook, Inc. (FB), Apple, Inc. (AAPL), Amazon.com, Inc. (AMZN), Netflix, Inc. (NFLX) and Alphabet, Inc. (GOOG), parent of Google. In the market reversal that was to follow, these same stocks would lead the way down.

Under the right conditions, a speculative advance in asset prices can take on a life of its own. In mid-2018, the FAANGs rose because fundamental investors wanted to own them for the companies’ long-duration growth prospects. Momentum investors, on the other hand, wanted to own the FAANGs simply because the prices were rising. With fewer stocks participating as breadth narrowed in the overall market, the FAANG group was the place to be. The futures of these companies seemed bright, and the lofty stock prices weren’t alarming for many investors as long as those prices kept going up.

That sense of eternal optimism was pierced in July, and stock-price momentum started to reverse. In response to a series of setbacks and business challenges, the share prices of Facebook, Netflix and Alphabet began to decline. In hindsight, the breakdowns in these stocks were warnings that investors in general were becoming more price-conscious and cautious. Amazon’s stock price peaked in September, while Apple’s followed in October. The Nasdaq Composite Index, of which the FAANGs are components, reached its all-time high in August.

Investors had good reasons to be optimistic about the FAANGs as businesses. These are innovative, growing companies with attractive future prospects. However, the prices of their stocks had become disconnected from the underlying fundamentals. By the end of 2018, Facebook and Netflix, respectively, had fallen -40% and -37% from their previous highs. Apple, Amazon and Alphabet experienced respective declines of -32%, -27% and -19%.

Although the FAANGs were the poster children of the fourth-quarter market rout, losses were broad-based across sectors and countries. As a result, these losses were strong reminders of how important it is to pay attention to a company’s stock price in addition to focusing on its fundamentals and long-term growth prospects.