In May, the Dow Jones Industrials (DJINDICES:^DJI) managed to post another solid performance, rising 0.8% and finishing the month at its fifth all-time record high close for 2014. Yet even though the Dow followed the broader stock market higher, about a dozen Dow components lost ground in May, and IBM (NYSE:IBM), Pfizer (NYSE:PFE), and Wal-Mart (NYSE:WMT) were among the worst performers during the month.

Source: IBM.

IBM fell 5.6% for the month as the tech giant continues to face problems from intense competition in the tech industry. Shareholders can't complain about IBM's willingness to share its profits, with the company having boosted its dividend for the 19th consecutive year, this time with a whopping 16% increase. Yet even with substantial share repurchases and dividend payments, IBM has investors nervous about whether it will be able to refocus its attention on more profitable business lines, as recent drops in revenue necessitate IBM finding higher-margin sources of sales in order to keep earnings up. That will prove increasingly difficult as competitors all flock to those more lucrative areas, and some therefore have concluded that IBM's best days might be behind it.

Pfizer dropped 4.4% as its attempt to buy out British drugmaker AstraZeneca proved unsuccessful. The potential deal would have had a number of positive elements for Pfizer, including economies of scale and cost synergies, a unified pipeline with arguably better prospects for long-term growth, and the possible tax advantages of a change in tax domicile to the U.K., where tax rates are more favorable. With Pfizer having given up on a bid, investors will have to wait at least six months to see whether the U.S. pharma giant renews its attempts to merge with its British counterpart -- unless Pfizer makes a major move in another direction in the interim.

Source: Wal-Mart.

Wal-Mart declined 3.1% as the retail giant has once again had to deal with slowing sales and concerns about its long-term growth prospects. Same-store sales in the U.S. fell during every single quarter of Wal-Mart's previous fiscal year and again in the first quarter, and operating margins in its international business have dropped dramatically in the past year as well. The question in the long run is whether Wal-Mart can use smaller stores as a way to get shoppers to make more frequent purchases, but it'll take time to see whether that strategy is effective. Until then, Wal-Mart will have to make do with an increasingly uncomfortable situation that has some of its shareholders wondering whether the stock will hold up as well in a future downturn as it did during the 2008 financial crisis.