A quarter-century ago, one of the most important stocks in the market lost a quarter of its value in a single day after the company drastically reduced expectations for its long-term profitability. Its main product was viewed as addictive and nearly immune to competition, and investors complacently believed stellar long-term growth was almost inevitable.

The company was Philip Morris, and April 2, 1993, became known as "Marlboro Friday" after it suddenly cut the price of its flagship cigarette brand by 20 percent, buckling to intense competition from generic smokes.

At least in broad outlines, the situation resembles the situation of Facebook today: Investors were conditioned to believe that Facebook's hold on its users was something close to an addiction and immune to bad press about fake news and misuse of customer data. Its shares ran up 23 percent this year to a new high and a market value above $600 billion.

Then came Wednesday night's mildly disappointing quarterly results and jarring forecast by management that spending would increase for quarters to come, profit margins will compress significantly and — perhaps — users in some regions were managing to kick their Facebook habit.

The benefit of hindsight tells us that, for Philip Morris — now called Altria, after its split with Philip Morris International — "Marlboro Friday" was a painful, but temporary, shakeout. The company managed to preserve market share and, eventually, work through massive legal liabilities and sharp declines in developed-world smoking rates. The company regained pricing power, produced massive dividends for shareholders and has delivered excellent long-term share-price returns.

However, Marlboro Friday also punctured investor confidence in other highly valued branded-consumer-goods companies, which in the '80s has gathered a reputation as can't-miss growth vehicles.

Of course, there's no saying the Street's readjustment to Facebook's revised outlook will track Philip Morris' experience from here. That stock took a year and a half or so to recoup those one-day losses. Facebook shares dropped 19 percent on Thursday — but back to prices last seen just a few months ago.

So it remains to be seen whether July 26, 2018, will come to be known as "Facebook Thursday."