On the surface, Friday's relatively flat finish by the S&P 500 Index (SNPINDEX: ^GSPC) might make it seem like it was a calm day on Wall Street. The reality: It was another painfully volatile day in a volatile week for tech stocks, which fell sharply enough to wipe out gains in almost every other sector. Amazon (NASDAQ: AMZN) shares fell almost 2%, leading big tech lower as almost every tech stock with a market cap above $200 billion closed lower to end the week. While tech was falling, every other sector except real estate gained in value, with industrials and materials sectors both up more than 1% to close out the week. Fertilizer company Mosaic, paper and packaging giant Avery Dennison, mining giant Freeport-McMoRan, and refiner Marathon Petroleum led their sectors higher, with all up 3% or more. Image source: Getty Images. Investors continue moving out of big tech stocks Today's tech stock sell-off continued a trend that's seen the S&P 500 tech sector lose more than 11% of its value since the market peak last week. That's easily the worst sector performance in the S&P 500 over that period, outpacing the declines of the telecom and energy sector that have also experienced big investor outflows. Here's how these sectors (as measured by the Energy Select Sector SPDR ETF, Technology Select Sector SPDR ETF, and Telecom Select Sector SPDR ETF) and the full index (as shown by the SPDR S&P 500 ETF Trust) have performed since Sept. 2, when the S&P reached its all-time high. XLE data by YCharts Every sector has sold off since the high, but the tech sector has driven the lion's share of the losses. Outsize tech sector sell-off wiped out broad gains almost everywhere else Here's how all the sectors closed on Friday: XLP data by YCharts The biggest, most valuable companies in the U.S. are largely technology companies, and as they move, so moves the broader market. That's how you can have one sector notably underperform a market in which almost all other sectors move higher and still finish at barely breakeven. Here's more context: The five biggest tech companies in the S&P 500, Apple (NASDAQ: AAPL), Amazon (technically classified as a consumer goods retailer, but it's just as much a tech company), Microsoft (NASDAQ: MSFT), Alphabet (NASDAQ: GOOG)(NASDAQ: GOOGL), and Facebook (NASDAQ: FB) had a combined market cap of $6.9 trillion at market close on Friday. The five biggest nontech companies, Berkshire Hathaway, Walmart, Johnson & Johnson, Procter & Gamble, and JPMorgan Chase, have a combined market cap of $1.9 trillion. Tech companies have a massive influence on U.S. stock markets, including the highly diversified S&P 500 Index. The sector has driven an outsize portion of investors' returns this year. Many of those investors have spent the past two weeks cashing out some of those gains in an uncertain economic environment as the coronavirus pandemic continues to weigh on the global economy. Get used to volatility This has become a constant refrain, but it's the reality that stock investors must come to terms with. Record volatility has been the hallmark of 2020, and that volatility is likely to remain with so many uncertainties -- economic, political, and health-related -- continue to cast long shadows over investors. Tech has been a big loser over the past couple of weeks, but it's also been the best-performing sector by far in this and prior years. As big tech becomes a bigger part of how we live and work in the years ahead, the longer trend of outperformance is likely to return. Stock investors would do well to remember that before joining others in the big tech exodus. 10 stocks we like better than AmazonWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now… and Amazon wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of August 1, 2020 John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Teresa Kersten, an employee of LinkedIn, a Microsoft subsidiary, is a member of The Motley Fool's board of directors. Randi Zuckerberg, a former director of market development and spokeswoman for Facebook and sister to its CEO, Mark Zuckerberg, is a member of The Motley Fool's board of directors. Jason Hall owns shares of Alphabet (A shares). The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Amazon, Apple, Berkshire Hathaway (B shares), Facebook, and Microsoft. The Motley Fool recommends Johnson & Johnson and recommends the following options: long January 2022 $1920 calls on Amazon, short January 2022 $1940 calls on Amazon, short September 2020 $200 calls on Berkshire Hathaway (B shares), long January 2021 $85 calls on Microsoft, long January 2021 $200 calls on Berkshire Hathaway (B shares), short January 2021 $200 puts on Berkshire Hathaway (B shares), and short January 2021 $115 calls on Microsoft. The Motley Fool has a disclosure policy.Source