To put that in perspective, Apple has lost more than the entire market value of Target, eBay, TJX, Northrop Grumman, or Ford Motor, which all have market values of less than $50 billion.
To be sure, $780 billion is still a massively large valuation for investors to put on a company — Apple is about $100 billion larger than Google-parent Alphabet. And there are many factors that can affect market valuations — investors may consider the company's expected future returns, sentiment about the stock market at large, whether they are maximizing short-term or long-term gains, dividends and overall macroeconomic conditions, just to name a few.
Nonetheless, Apple shares closed down nearly 1 percent on Friday with slightly heavier-than-average trading volume, ending the week down 5 percent. The stock had the most negative point impact on the S&P 500, according to FactSet.
Gene Munster, an investor at Loup Ventures and a former top Apple analyst, has said that Apple's shares could see a 5 to 10 percent pullback after the release of the latest iPhones, even if the products were well-received (CEO Tim Cook says they have been.)
"The simple reason is this: The stock's up 50-plus percent in the past year because investors have been anticipating the return to growth of the iPhone. As soon as that product comes out, people are going to shift their focus to the March and June quarters of next year. That's when the iPhone cycles are made or missed," Munster told CNBC earlier this month. "So there's naturally going to be some people taking some profits."
As of Friday, Apple shares are still up more than 30 percent over the past year.