What happened

No two ways about it, Nasdaq stocks had a bad day today, falling 9.4% by close of trading -- and not just "Nasdaq stocks," but that most Nasdaq-y of Nasdaq stocks, Nasdaq (NDAQ 0.10%) the stock, which closed down 10.3%.

Meanwhile, electronic payments and transactions processor Euronet Worldwide (EEFT 0.58%) fell 12.8%, and banker SVB Financial (SIVB.Q 2.00%) was down 7.9%.

Man crouching and holding head under a falling stock chart

Image source: Getty Images.

So what

What do these three stocks have in common? All are, of course, broadly considered "financial" stocks, and when stock markets fall broadly, as they did today, investors may naturally extrapolate that weakness to the financial system in general and start selling financial stocks en masse.

And yet, it's notable that none of the three companies named above had any bad news of their own to report. To the contrary, the only actual news I can find discussing any of the three is news of a positive sort: This morning, Bank of America took one look at how far Nasdaq, Inc., had fallen in the past three weeks (down 15%), and decided it was finally time to upgrade the stock to "buy."

Now what

That decision by one big banker didn't prevent the rest of Wall Street, however, from deciding to "sell" Nasdaq instead. It didn't prevent a stock that was down 15% already from falling another 10%.

And that may be the real lesson investors need to draw here. Just as weak or nonexistent profits didn't prevent investors from buying shares in sexy, fast-growing tech companies despite their increasingly disturbingly stratospheric valuations during the bull market, it may take more than simply an improved stock valuation and an endorsement from a big bank to attract buyers back into Nasdaq stock again (or into Euronet or SVB Financial, either).

For savvy buyers, though, this can present an opportunity to buy stocks at bargain prices when no one else wants them. After today's market rout, for example, Nasdaq, Inc., shares are selling for less than 19 times trailing earnings, Euronet costs less than 14, and SVB Financial looks positively enticing at a mere 6.3 P/E.

The right time to get greedy, as the saying goes, is when others are fearful -- and the fear is positively palpable today.