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.

On a winning day for the overall stock market, you'd expect many individual stocks to post impressive gains. But when stocks jump more than 10%, there's usually a good reason why. Today, let's take a closer look at Veeva Systems (NYSE:VEEV), Geron (NASDAQ:GERN), and MGIC Investment (NYSE:MTG) to find out why they did so well today.

Veeva Systems climbed 86% after coming public this morning at $20 per share. The reason is simple: Veeva is in the perfect niche of a promising industry, creating cloud-based software for medical providers. Cloud computing in general has gained in popularity as businesses seek alternatives to making large investments in private IT networks. Moreover, with health-care reform having reemphasized the importance of electronic medical records, Veeva should be able to ride the trend of health-care providers and large pharmaceutical companies looking to modernize their systems.

Geron soared 40% as the company disclosed that results of a study of its imetelstat treatment for myelofibrosis would be presented at the annual meeting of the American Society of Hematology. The move comes two weeks after Geron completed the sale of its once-controversial stem-cell assets, leaving itself better focused to concentrate on imetelstat's potential.

MGIC Investment climbed almost 15% as investors celebrated the mortgage insurer's third quarter earnings report. For the second straight quarter, MGIC defied initial expectations of a quarterly loss, instead posting a profit of $0.04 per share. Yet analysts observed that much of the surprise came from a reduction in the amount MGIC set aside for loss reserves. Admittedly, rising home prices have boosted the risk-reward equation in MGIC's favor over the past year, but one-time changes in loss reserves shouldn't be confused for sustainable earnings based on MGIC's insurance business.