Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Optimism about a positive start to earnings season took over the stock market today, with the Dow posting its second straight day of triple-digit gains. But even with the S&P 500 hitting a new record high, Nu Skin Enterprises (NYSE:NUS), Qiwi (NASDAQ:QIWI), and ExOne (NASDAQ:XONE) all posted severe declines after company-specific news hit their respective stocks hard.

Nu Skin fell 16% as investors responded to allegations from a state-owned Chinese newspaper about the company that many interpreted as accusing the company of running an illegal pyramid scheme. Nu Skin responded to the allegations, arguing that the article contained "inaccuracies and exaggerations that are not representative of Nu Skin's business in China" and expressing its commitment to work with regulators to resolve any concerns that the article might raise. Given the perception that many investors have regarding apparent similarities between Nu Skin's business and Herbalife's (NYSE:HLF), however, it's easy to understand why shareholders would be quick to pull the trigger on even the hint of trouble plaguing Nu Skin.

Qiwi plunged 17% after concerns arose about possible Russian regulations that could limit the payment-systems company's ability to grow its business. With anti-terrorism laws possibly imposing a ban on payments across international borders, the usefulness of Qiwi's payment-services network could be greatly lessened. Even after the drop, Qiwi shares have still almost tripled from levels set right after its May IPO.

ExOne fell 9%, reversing recent optimism about its growth prospects after the 3-D printing company dramatically downgraded its guidance for full-year 2013 revenue. ExOne believes that the shortfall of 12% to 17% is more a matter of timing than actual lost sales, investors weren't willing to give the company the benefit of the doubt that it can produce revenue growth of 40% to 50% in 2014. Investors in 3-D printing stocks need to understand the huge expectations built into share prices at current levels and be prepared for turbulence at the slightest sign of possible negative news.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.