In Good to Great, you explored the incredible amount of effort it takes to begin to transform an organization. But you proposed that once it is started, the momentum builds like a flywheel. You're now doing some research on the downshift from "great" to "good". How difficult is it to sustain that momentum over time, particularly in times of great market shifts?

Our research indicates that the flywheel concept applies as much in times of change as in times of stability, perhaps even more so. Over the long course of history, a great company is built by a series of good decisions executed with supreme excellence, accumulating one on top of another over a long period of time. No decision or event, no matter how big, accounts for more than a small portion of the total outcome. Greatness is a cumulative process, even in times of dramatic change. And never forget: the most important flywheel decisions are people decisions. If you get the right people, they can adapt to a changing world.

The very nature of our research method — studying those that attained and sustained greatness in contrast to those in similar circumstances that failed to become great (or failed to sustain it) reduces the role of circumstance in explaining outcomes. If one company rises and the other falls, yet they both have similar circumstances at the start of the inflection, then the answer cannot be circumstance.

My colleague Morten Hansen and I are nearing completion of a six-year research effort studying companies that went from startup to greatness in environments characterized by turbulent disruption. We've deliberately selected companies in the most severely turbulent industries, using the following climbing analogy: If you wake up in the security of base camp and a storm moves in, you'll probably be fine. But if you find yourself at 27,000 feet as a vulnerable little speck on the side of Mount Everest, where the storms are bigger, faster moving, inherently unpredictable, and the environment less forgiving, a storm just might kill you.

Our research examines companies that prevailed in such environments in contrast to those that did not prevail in the same brutal, turbulent, rapidly changing environments. No matter how we slice it, greatness — creating it and sustaining it — is a function first and foremost of conscious choice and discipline, not circumstance.