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.

Fun fact: the S&P 500 Index (^GSPC 0.02%) has fallen each and every day the stock market has been open for trading in 2014. Thankfully that's not really so ominous, since Wall Street's only seen three days of trading in the nascent year. While the severe winter weather around the U.S. -- currently slowing travel and commerce -- will eventually abate, longer-term questions about the labor market and monetary policy remain as chief concerns for investors looking to the year ahead. But today the horrific weather was the headline as thousands of flights were cancelled and the S&P 500 fell 4 points, or 0.3%, to end at 1,826. 

The absolute worst performer in the 500-stock index, losing nearly a tenth of its value in just six and a half hours, was First Solar (FSLR -1.46%), which fell 9.7% Monday. Shareholders can blame Goldman Sachs analyst Brian Lee for the painful portfolio-busting downgrade he gave First Solar today, citing a lack of diversification between the utilities and residential markets. Lee, who also slapped a $45 target price on shares, thinks First Solar's extreme bias toward utilities as end-users is shortsighted. Solar energy is a high-risk, high-reward industry, but with First Solar's revenue surging by 170% between 2008 and 2012, the company isn't exactly in any existential danger.

Playing its role as antagonist like few other investment banks can, a Goldman Sachs downgrade was also the primary reason for Celgene's (CELG) 4.2% dip today. The $67 billion New Jersey-based biotech was one of several big names in its industry to suffer from Goldman's sweeping biotech sector downgrade Monday. The Wall Street bank feels valuations are, broadly speaking, stretched beyond the point of being attractive. Investors are hoping that Celgene's blockbuster oncology treatment Revlimid, as well as the FDA-approved Pomalyst, will continue to prove doubters wrong in 2014.

Interestingly, AbbVie (ABBV -1.03%), the $80 billion biopharmaceutical company out of Chicago, also finished as a laggard today, losing ground even after one bank boosted its price target on the stock. AbbVie stock shed 3.7% even after UBS raised its target price by $10 to $56 per share, underscoring the fact that while analysts may move markets, they're not the visionaries some hold them to be. While it will be tough to match the 60% gains AbbVie saw in 2013, a portfolio that includes the top-selling drug in the world can't be too shabby.