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

What: Shares of fuel cell company Plug Power Inc (NASDAQ:PLUG) plunged as much as 12% today after reporting fourth-quarter earnings.

So what: Revenue for the quarter jumped 169% to $21.5 million but fell well short of the $26.3 million estimate from analysts. On the bottom line, net loss shrunk from $28.9 million a year ago to $7.2 million but was helped by some one-time items. On an adjusted basis, net loss was $13.3 million, or a loss of $0.08 per share, which fell short of the $0.04 loss Wall Street expected.  

Now what: Operating conditions are certainly getting better for Plug Power but not at the rate investors had anticipated. That will happen when your stock is up 1,100% over the course of two years.

Expectations from investors may have gotten too high and the stock price likely did as well. That's why even strong growth can result in a new 52-week low for a stock. I don't think this quarterly report is a fundamental reason to change your investment thesis, but it may take longer to ramp up product shipments and profits than previously expected, so I would lower expectations for 2015 and hope management can beat expectations as the year goes on.