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.

The Dow Jones Industrials (DJINDICES:^DJI) began the day climbing through the 16,000 level once more, only to fall back once more and finish the day down by nine points at 15,967. With well-known financial-industry insiders advising caution as the stock market continues its nearly uninterrupted run higher, investors seemed reluctant to press on to new records. SolarCity (NASDAQ:SCTY.DL), Stratasys (NASDAQ:SSYS), and Best Buy (NYSE:BBY) were just a few of the high-flying stocks that got punished much more severely today, as the highest-momentum stocks once more came under fire. Let's see what we can learn about these stocks and their drops today.

SolarCity fell 8% as a key member of the Senate Budget Committee wrote a letter to the Treasury Secretary questioning whether the residential solar company inflates the value of the costs it reports, thereby increasing the amount of subsidies that it receives on behalf of taxpayers who install solar systems. Sen. Jeff Sessions suggested that such practices could be detrimental to investors as well as to the government, and the potential controversy involved clearly spooked shareholders who had previously seen SolarCity's huge growth in volume expectations as a reason to get more optimistic about the company.

Stratasys declined 9% on a bad day for 3-D printing stocks in general, as the company's rivals also posted big losses. Despite no company-specific news, the immense volatility in the share prices of Stratasys and its peers lends itself to sharp corrections, especially after the gains that the stocks have seen so far this year. Despite the hair-trigger reflexes of many traders, long-term investors have to realize that truly market-moving news on Stratasys and other 3-D printing stocks won't come on a daily basis.

Best Buy plunged 11%. The electronics retailer reported fairly favorable results for its October quarter, with earnings that beat expectations and a small rise in same-store sales. But looking forward, Best Buy said that its competitors are offering substantial discounts going into the key holiday season. That gloomy guidance took some of the wind out of Best Buy's sails, especially given the huge rise the stock has seen recently, and investors might see further drops in the shares if the holidays go as badly as Best Buy seemed to imply today.