Amazon’s bid to buy Whole Foods has shaken up the grocery business, and it is forcing all retailers to reset their expectations about Amazon’s reach.

But like any merger, there’s risk involved. Amid the excitement of a mega-deal it’s easy to overlook an uncomfortable fact: Most mergers fail.

Research has shown that mergers fail more than half the time. Some studies put the failure rate as high as 80 percent.

For Amazon, there is strong commercial logic for buying Whole Foods. It gets physical locations in key markets, plus access to an attractive customer base. Amazon also gets a trove of data to help it crack the code for online grocery shopping, a market that could be as large as $100 billion by 2025.

But fulfilling the deal’s potential requires great execution, and on a scale that Amazon has never attempted. Amazon has made dozens of acquisitions, but Whole Foods, at $13.7 billion, is its largest by far.

Mergers fail for lots of reasons. Sometimes the companies are a poor strategic fit. Or the buyer fumbles the due-diligence, or pays too much. But two factors are almost always on the list when mergers don’t succeed – communication and culture.

Companies often underplay the importance of communication in a merger. Sure, there is usually some when they announce the deal, and plenty of champagne and celebration, too. But communication in the post-merger stage is as important, and it’s often overlooked.

Mergers mean change for employees, customers and business partners. Even well received deals can create a crippling sense of uncertainty. Communication is a way to keep it in check, and it is most effective when it does three things:

First, it should use clear language – no buzzwords, no vague phrases.

Second, it should address important issues, not trivia. Who’s in charge? What’s happening with clients? Where is the company investing, and where are cost savings coming from?

And third, communication should provide a roadmap. What are the goals for the business? How fast is it progressing toward them? Is the integration in its early innings or farther along?

Communication can also play a role in bringing together the two corporate cultures. This is can be the most difficult aspect of making a merger work.

But what does “corporate culture” mean, exactly? Sandy Weil, the former chairman of Citigroup, once dismissed the whole idea, saying all the talk about culture only reminded him of yogurt. (Citigroup nearly collapsed a few years later, so maybe he should have paid more attention to it.)

A corporate culture is a set of unwritten rules that guide how people behave. It’s a way of doing things, covering how a company interacts with customers, how it handles problems and how its employees treat each other. It’s not in a manual or etched in a stone tablet in the lobby. But culture is a powerful influence on employee behavior.

Getting the cultural fit to work can yield a big payoff, too. According to Harvard Business School Prof. Jim Heskett, culture accounts for as much as half the difference in operating profit between similar organizations.

CEOs with merger experience recognize this. Jack Welch of GE epitomized the hard-nosed, by-the-numbers CEO, yet he saw the importance of culture:

“No matter how good the numbers look, culture matters as much as financial profile.

Lou Gerstner of IBM also came to recognize that culture is essential to the success of a business:

“Until I came to IBM, I probably would have told you that culture was just one among several important elements in any organization’s makeup and success — along with vision, strategy, marketing, financials, and the like… I came to see, in my time at IBM, that culture isn’t just one aspect of the game, it is the game.”

So if communication and culture are important, how should Amazon and Whole Foods proceed if their merger happens? Here are three suggestions:

First, decide how much integration is appropriate. Integrating the businesses completely makes sense for some acquisitions, but for others continued autonomy might be best.

Will the Whole Foods brand continue or will appear on storefronts instead? Will Amazon’s hard-driving workplace take hold at the grocer? Those decisions should come early in the process.

Second, use data. Amazon and Whole Foods can only know if the integration is working if they are measuring it. That means going beyond the financial metrics to gather data on things like staff retention and customer satisfaction. Merger success doesn’t happen overnight, and there will be twists and turns along the way. Collecting the right data lets you know where you are.

Third, allow no elephants. Managers sometimes avoid tackling the difficult issues even when they’re clear to everyone. Closing stores, selling assets or making new leadership appointments are tough but necessary decisions. A management team that ignores the big issues will see its credibility evaporate.

Combining two organizations after a merger is never easy. But getting communication and culture right can help improve the odds for success.

For Amazon and Whole Foods, it could mean the difference between whether they write a new chapter in online commerce or become another cautionary tale about ambitious mergers that failed to live up to their promise.