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 page on the calendar might have changed, but stocks continued their terrible 2014 even as February began. Losses of between 2% and 3% plagued the major market average as investors grew fearful of signs of sluggishness in the long-resilient U.S. economy. Among the worst performers on the day were SunPower (SPWR -1.02%), Alpha Natural Resources (NYSE: ANR), and United Online (NASDAQ: UNTD).

SunPower (SPWR) dropped 10% on a bad day for solar stocks generally. Despite having obtained $220 million in solar lease financing capacity from Merrill Lynch last week, SunPower has seen its valuation skyrocket over the past year, with shares having quadrupled from year-ago levels. With concerns about the manufacturing sector weighing on the overall market, some investors might well simply have decided that SunPower and several of its solar peers represented a fertile ground to take profits.

Alpha Natural Resources (ANR) fell 8% as the company joined most of its coal-mining peers with substantial declines today. Weaker manufacturing directly means less energy demand, and even though cheap natural gas has supplanted coal's place in many manufacturing processes, every little bit of lost demand at this point puts Alpha Natural and other coal companies in a more difficult situation. Even though the company received recognition for its environmental stewardship today, Alpha Natural needs industry conditions to improve in order to see its stock respond favorably.

United Online (UNTD) plunged 12% after the Internet service provider discontinued its dividend after the market closed last Friday. The stock had yielded 5%, making it a popular choice among yield-hungry investors. But United Online said it wants to free up cash for future growth initiatives. Combined with possible future share buybacks, the company believes that it still offers solid shareholder value for its shareholders -- even if the move disappoints those who had come to depend on quarterly income.