Facebook's $120 billion stock drop — a company's biggest one-day loss of market value in U.S. history — isn't solely about Facebook, Felix Salmon, Slate columnist and "Slate Money" podcaster, writes in a special guest analysis for Axios.

Why it matters: The 19% plunge reflects the fragility of the tech sector as a whole. And it's all the proof you need that tech investors have moved from greed to fear.

Absent the shortfall from what had been promised, the Facebook earnings reported Wednesday evening were objectively excellent, up 32% year-over-year, with revenues up 42% (and up 11% quarter-over-quarter).

• And while user growth has pretty much flatlined in the mature markets of the U.S. and Europe, it’s been obvious for a while that those regions were running out of new customers.
• Which means that the panicked aftermarket flight was partly a function of investors taking the excuse to sell near all-time highs. (Although the rest of the tech stocks held their ground: Google nailed its numbers and its stock was rewarded.)

Logic behind the loss:

• Facebook stock is now back to where it was after the Cambridge Analytica scandal broke, and the negative headlines aren’t going away.
• The best-case scenario for investors is that Facebook will hurt its earning power by throwing so many workers and so much money at the problem of fake, dangerous, and toxic content that it will go away. That’s going to be a huge ongoing expense.
• The worst-case scenario is that Europe and other jurisdictions ban all targeted advertising, the Facebook earnings machine.
• Valuations are stretched across the sector, and shorts, especially in Tesla and Netflix, have already been hurt badly. Short squeezes are great for momentum, but they rarely last very long.

Be smart: The broader narrative has turned, decisively.

• The single most important thing any tech investor should do is to go see the new Boots Riley film Sorry To Bother You, which nails the mood of the nation, and its mistrust of Big Tech: People who invested in utopian visions are beginning to feel bait-and-switched.

P.S. An eye-opening way to look at the $119 billion loss, per the Wall Street Journal (subscription): That market value is "larger than 457 of the 500 companies in the S&P 500."

• Per AP, "the collapse eclipsed Intel's decline of $91 billion in September 2000, without adjusting for inflation. ... Mark Zuckerberg saw his net worth fall by roughly $16 billion ... It was Facebook’s worst trading day since going public in 2012."