Photo credit: Flickr user Paul Lowry.

After six straight years of gains, investors have high expectations for the stock market in 2015, as continued economic expansion has made the U.S. look far more attractive than most other markets around the world. Yet stocks haven't gotten off to the best start this year, with the Dow Jones Industrials (DJINDICES:^DJI) opening Monday's session with a loss of more than 230 points as of 11:45 a.m. EST. Many analysts have blamed the plunging energy markets, which continued to see further losses in the price of oil Monday. But the question smart investors are asking is whether the real cause of today's declines is more complicated than energy-related worry.

Looking beyond energy
Clearly, the energy sector has played some role in the market's nervousness lately. Oil prices fell almost $2 per barrel Monday morning, with West Texas Intermediate falling below the $51 per-barrel mark. That has had a huge downward impact on Dow energy components ExxonMobil (NYSE:XOM) and Chevron (NYSE:CVX), both of which were among the Dow's three worst performers with respective losses of about 3% and 4%. Furthermore, the second-order impact of energy's slowdown has hit other stocks, most notably Caterpillar (NYSE:CAT), which is also down about 4% Monday morning.

Photo credit: Flickr user Christopher Griner.

Yet there are quite a few other crosscurrents in the financial markets that have contributed to today's sense of uncertainty. After having climbed steadily since the financial crisis, the net negative credit balances that investors have in their brokerage accounts have reached record levels and are now starting to raise concerns about overuse of margin debt among ordinary accountholders. Moreover, with potential short-term interest-rate hikes coming as soon as later this year, paying interest on margin debt could soon become a much bigger burden.

At the same time, the strength in the U.S. economy has overshadowed underperforming economies elsewhere in the world. The euro fell to its lowest level against the U.S. dollar in nearly a decade, as echoes of the Greek financial crisis several years ago continue to sound in light of upcoming elections. With many areas of Europe still in recession and the Japanese economy still struggling under the weight of a new sales tax implemented last year, investors question how long the U.S. can stand out from the global crowd and continue to climb.

After another winning year in 2014, it shouldn't come as any shock if the Dow gives back some of its gains early in 2015. But rather than focusing solely on energy as the obvious cause of market jitters, you need to look at the entire financial picture in order to put any market declines in perspective. Otherwise, the conclusions you draw could lead you to make mistakes in how you invest this year that you'll later regret.