By Ann Meyer
 Here's why they occur and how to avoid them. 

Cold, hard numbers frequently spur mergers, as companies strategically invest in a competitor or supplier to gain capabilities, extend their reach or improve efficiencies.

Yet those same numbers can't predict the success of the merger, and studies suggest most deals fall short of expectations. Often, the problem is a culture clash.

When investment bankers crunch the numbers, they often don't take into consideration that people ultimately can make or break a merger. Without buy-in from middle managers and front-line workers, integrating two entities is likely to flop.

"Culture is one of those soft things people frequently underestimate when you're getting into an acquisition or merger," says Scott Whitaker, president of Whitaker & Co., an Atlanta management consulting firm. "It can delay things, cause headaches and employee morale issues...It can affect every success metric you've outlined."

McKinsey & Co. reports that executives know that culture plays a role, with 50 percent of respondents to a 2010 survey saying cultural fit was central to a value-enhancing merger. But 80 percent also said culture was hard to define.

"Culture is how we do things around here. It's the simplest way to say it."

–Logan Chandler,

Schaffer Consulting

"Culture is 'how we do things around here.' It's the simplest way to say it," says Logan Chandler, partner at Schaffer Consulting in Stamford, Conn. "It's critically important and not well understood."

Part of the confusion stems from the fact organizations typically have a formal culture defined by written policies and procedures and an informal culture that reflects "this is the way we get things done," says J. Neely, vice president at Booz & Company in Cleveland.