This post is chapter 1 of the book 'The Opposable Mind' written by Roger Martin. You can read the high level review of the book in THIS POST. Please read it before you read this post.
In business, we often look at decisions as series of either - or propositions or trade offs. However, exceptional leaders have the predisposition and ability to hold two diametrically opposite ideas in their heads and they are able to produce a synthesis that is superior to either of the opposing ideas. Roger Martin calls this 'Integrative Thinking'.
To develop integrative thinking, the author looks for a metaphor which can provide insight into the thinking process of integrative leaders. He lands upon the concept of 'opposable thumb'. Human beings are the only creature in the earth with the capacity to put tension between the thumb and other fingers. By systematically developing their ability to use the opposable thumb, human beings are able to do things that no other creature can do, like writing, for example.
Roger Martin calls the ability of people to keep two opposing ideas in their minds as the 'Opposable Thumb'.