What's the most destructive force in the tech world, the thing that has nearly killed BlackBerry, pushed Dell to go private, and made a mess of Microsoft?

Conventional wisdom in Silicon Valley would finger one of the following technologies: smartphones, tablets, social networks, 'the cloud,' app platforms, or some other inscrutable bit of jargon.

Actually, though, the most destructive, unpredictable, and fickle force in the tech industry is much closer to home: It's you and me and everyone we know.

In the not-too-distant past, most of us didn't have much of a say in the technologies we used every day. Instead, your gadgets were delivered to you from afar, chosen by faceless people in nameless offices based on criteria that you didn't understand. If you went to buy a cellphone, you'd be presented with a handful of devices that were approved for your carrier, and they were all locked down in ways that prevented you from running apps that conflicted with the carrier's business plans. In your living room, you had a cable-company issued set-top box, and if its video-on-demand system didn't feature your favorite show, you'd better find a new favorite.

At the top of the tech food chain sat your boss--or, more specifically, your company's chief information officer. Most of the world's tech devices were purchased for corporate use, and IT guys tended to make decisions based on security and price rather than user-friendliness. Tech companies that catered to CIOs rather than users tended to thrive. That's why--whether you liked it or not--your office computer was made by Dell, it ran Windows and Office, and why your company-issued phone was a BlackBerry.

Then, more or less overnight, a series of technological and marketing revolutions--like ubiquitous broadband Internet and the lure of consumer devices such as the iPhone--completely upended the market for technology. Over the past few years, for the first time, we 'end users' have been allowed to choose the tech we want to use at home, on our wireless networks, and, crucially, at the office.

Just a few years ago, BlackBerry Ltd.'s executives were promising that their gadgets would win out over rivals because the BlackBerry was 'way ahead' on 'CIO friendliness.' But the beleaguered execs hadn't considered that CIOs themselves might lose their power. As employees began demanding the ability to use the phones, tablets, and apps that we had at home, the most forward-thinking corporations found ways to allow a whole new class of technology onto their networks.

Now you could use an iPhone instead of a BlackBerry, an iPad instead of a Dell computer, and Google Docs instead of Word. In the end, CIO friendliness couldn't help BlackBerry one bit.

BlackBerry's downfall and the struggles of Dell and Microsoft offer an object lesson for any firm trying to crack the 'enterprise' tech market. It suggests that even if you want to sell technology to CIOs, you can't forget employees, the people who will actually have to use your stuff.

'It's an amazing lesson in what happens when one set of buyers implements a technology for another set of users, without a care or sensitivity for what the users were going to need to get their jobs done,' says Aaron Levie, the CEO of Box Inc., one of the Valley's most promisingenterprise startups.

Box sells a cloud-storage platform to big corporate customers. Yet unlikeenterprise companies of yesteryear, Mr. Levie says his engineers and product teams can never stop thinking about employees--the people who'll actually be using his stuff.

Box exemplifies a strategy I once termed the Facebookization of the enterprise: 'We've combined the product-designed mind-set of Google or Facebook with the sales strategy you'd see at a firm like Salesforce.com and the better parts of Oracle,' Mr. Levie says.

Consider Box's latest product, a document-collaboration app called BoxNotes. When two people in different locations are typing on the same document, BoxNotes highlights each user's changes by showing their faces--a trick that Mr. Levie proudly admits was inspired by Facebook's ChatHeads messaging feature.

Even in its approach to sales, Box departs from the enterprise-tech model of the past. 'Until recently, we would actually avoid talking to the CIO or another IT buyer at a company,' Mr. Levie says. Instead, Box would approach a company's head of marketing or sales--and once people in those departments started using Box, employees would spread the word throughout the company, eventually forcing the IT department to adopt Box.

Call it the case of the incredibly shrinking IT Guy: In the past, CIOs and their staffs had a reputation for being snarky, geeky guys who were always looking for ways to tell employees what they couldn't do. Now, at the most progressive companies, the tech department's main job isn't to say no. Instead, it's to find a way to let employees safely run any device or program they like. The thinking goes like this: Employees are most productive when they're allowed to work with the tools that make them happy.

According to the research firm CB Insights, startups focused on the enterprise rather than consumer marketplace are now seeing renewed interest in the Valley. These companies would be wise to keep the BlackBerry lesson in mind. Any firm whose products will mainly be used by nontechies within the organization--that is, companies selling customer-relationship management software, sales software, analytics software--will need to create tools that work just as well as the consumer-grade tech we get from the likes of Apple and Google.