A key to understanding the massive and unexpected $26.2 billion acquisition of LinkedIn by Microsoft can be found in the letter LinkedIn CEO Jeff Weiner wrote to his employees explaining the deal. “You might feel a sense of excitement, fear, sadness, or some combination of all of those emotions,” he wrote. “Every member of the exec team has experienced the same, but we’ve had months to process.”

That range of emotions also sums up how investors and customers feel when a big merger takes place. First, there’s excitement at the opportunity to help two companies keep growing. There’s fear around the job cuts that could follow and the high risk that, once integrated, the marriage fails to reach its potential. And sadness when you remember that between 70% and 90% of M&As fail to achieve the benefits they initially promised.

The stakes are high for Microsoft and LinkedIn. This is one of the biggest tech M&A deals ever, topping even Facebook’s $22 billion purchase of WhatsApp. On paper, there is indeed reason for initial excitement about this deal, largely because there is little operational overlap between the two companies. Yet they have complementary, even converging, strategies.

This means jobs cuts could be minimal, and that LinkedIn can remain independent inside Microsoft – as WhatsApp and Instagram have within Facebook – while the potential for each company to help the other grow is evident. But reaching that potential depends on how exactly the two are integrated over the next couple of years. The devil, as always, will be in the details.

In announcing the acquisition, Microsoft and LinkedIn summarized the benefits as meshing LinkedIn’s 433 million members with the professional cloud that Microsoft CEO Satya Nadella has been building for Microsoft’s future. LinkedIn’s stock has tumbled this year as it seemed to run dry of ways to monetize its network. Microsoft has been looking for ways to get more people using cloud apps like Office 365, Skype and Cortana.

Among the examples Nadella and Weiner gave in a conference call with investors: LinkedIn could give Microsoft’s productivity software the social-network piece it’s always lacked, while Office and Outlook could make it easier to keep your LinkedIn profile updated. LinkedIn’s newsfeed could draw on, say, your Calendar schedule to become more engaging, which could in turn boost its ad revenue. Cortana could scour your LinkedIn network to create a quick brief about who’s attending your next meeting.

The core idea is to draw on more data to boost productivity and make both LinkedIn and Microsoft more essential to the workday. But whenever personal data is the lifeblood of a business plan, privacy concerns emerge. Nadella said that “nothing will get connected or linked without users opting in” but also extolled the potential of applying machine learning to user data in order to generate more recruitment leads and help sales forces drum up more business. Bosses will also have a clearer view of who employees are talking to and how they’re spending their time.

For all the potential benefits that Microsoft and LinkedIn could reap by joining forces, the news is being greeted with some skepticism. One analyst pointed out that the deal could be jeopardized if rival bidders emerge or if LinkedIn’s earnings disappoint before the deal closes. Others reminded investors of Microsoft’s poor track record with big acquisitions like aQuantive, Skype and Nokia. According to Barron’s, Roger McNamee, a veteran tech investor, questioned whether LinkedIn users would flock to Office 365. “It’s really simple,” McNamee added, “Big deals don’t work.”

Meanwhile, the sheer size of the proposed acquisition is huge enough to have other impacts. An early one is to steal the media thunder from Apple as it launches its closely watched developer conference. A more substantial one is to make it tougher for Facebook to muscle its way in to work-oriented social networks, now that LinkedIn has Microsoft’s considerable resources behind it. And it could spur a wave of tech acquisitions, particularly among emerging productivity startups like Slack and struggling social networks like Twitter. Twitter’s stock was up as much as 9% after the LinkedIn buyout was announced.

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