An expert's job is to be right — to solve the client's problems through the application of technical and professional skill. The advisor behaves differently. Rather than being in the right, the advisor's job is to be helpful, providing guidance, input, and counseling to the client's own thought and decision-making processes. The client retains control and responsibility at all times; the advisor's role is subordinate to this, not that of a prime mover.

The world of management theorists remains exempt from accountability. In my experience, for what it's worth, consultants monitored the progress of former clients about as diligently as they checked up on ex-spouses (of which there were many). Unless there was some hope of renewing the relationship (or dating a sister company), it was Hasta la vista, baby. And why should they have cared? Consultants' recommendations have the same semantic properties as campaign promises: it's almost freakish if they are remembered in the following year.

If you know one (of anything), that's it: You know one. But if you know two, you know much, much more than two. With two computer languages, not only do you know both languages, but you also know what makes them similar, what makes them different, what you like best and least about each, and how each is better suited for certain tasks.

Call it the "epiphany of multiples." I'm not a linguist or a musician, but I have been told by those who are that the same miracle holds true in these fields: Learning your second language or instrument opens a door to learning multiple languages or instruments more easily than the first or the second.

Similarly, consultants have often worked in many companies, countries, industries, functional areas or technologies. This wide-ranging exposure has given them the perspective that can generate valuable innovations. This perspective, in turn, helps them tackle challenges or realize opportunities that would be overlooked by someone with twice the experience but without the epiphany of multiples.

In McKinsey's world, all of life is one of two things: strategy or organization.