The single best predictor of M&A integration success is the length of the transition period.

The longer you take to integrate, the closer you live to the edge. Disappointing deals correlate highly with slow consolidation.

Decades of merger experience prove this. The turtle may win the race in fairy tales, but not in the grinding, gut-wrenching, high-risk game of merger integration. We’ve been saying this for years, and it’s coming close to being accepted now as conventional wisdom. Here’s the problem—companies still demonstrate big differences of opinion regarding what “fast” really is.

Some organizations, we all know, are notoriously slow. They can speed up significantly, and still be dragging their feet to a dangerous degree. Who comes to mind? Utilities. Some insurance companies. Governmental agencies. Not-for-profit organizations. And some of America’s corporate giants that lumber along like cargo planes in a competitive world better suited for fighter jets.

In fact, even those companies that could consider themselves respectably fast in the way they merged a decade ago may be sluggish by today’s standards.

Most mergers are still taking much longer than they should. Sure, companies are picking up the pace, but the world of change is accelerating even faster. So before they finish the consolidation, they get hit by other changes that demand management’s attention and that suck up financial resources. The more leisurely you proceed with the merger integration process, the more you’re likely to end up a victim of change overload.

We still see executives—highly capable business people—who sit down, reason among themselves, and conclude that, by golly, they’re going to take the time needed to do it right. Sounds good in theory, fails miserably in practice...