Breaking an old business model is always going to require leaders to follow their instinct. There will always be persuasive reasons not to take a risk. But if you only do what worked in the past, you will wake up one day and find that you’ve been passed by.

Because if the decisions you make about where you invest your blood, sweat, and tears are not consistent with the person you aspire to be, you’ll never become that person.

Because these firms listened to their customers, invested aggressively in new technologies that would provide their customers more and better products of the sort they wanted, and because they carefully studied market trends and systematically allocated investment capital to innovations that promised the best returns, they lost their positions of leadership.

Quite often startups were first out of the gate with a sustaining technology. But somehow the leaders got the technology and stayed atop their industries. Sometimes they acquired the startup; sometimes they just developed the technology as a follower and used their muscle and mass to win. But they always won.

How could Digital's collapse be so precipitous? It's because, in many ways, financial performance data is misleading. As you move up to the top of the market, you're getting rid of the less profitable products at the low end and adding business with more attractive margins at the high end. The rate of unit volume growth might be tapering off as you pursue these smaller markets, but your margins actually look better. So Wall Street rewards your stock price until you hit the ceiling.

History is littered with great firms that got killed by disruption. Of course, the personal computer, a technology that first took root as a toy, got Digital Equipment Corporation. Kodak missed the boat for a long time on digital imaging. Sony was slow to get MP3 technology. Microsoft doesn't know what to do with open source software. And so on.

In my first career I had founded my own company, with a group of MIT professors, before coming to Harvard to finish my doctorate, and so I had a deep respect for the brains, talent, and dedication of managers. That made it hard for me to believe the attributions in the business press that stupid management was to blame. So I looked elsewhere for an explanation.