In the 1930’s and 40’s, Gestalt psychologists made clear the premise that the first important step to solving a problem is identifying and defining the problem. When a group is not all on the same page with respect to understanding the problem to be solved, they are effectively solving different problems. Small wonder that those groups with less overall insight into each others’ perspective, emotional or otherwise, are less effective. Also one of the reasons why groups with leaders that are better able to pick up on disparate perspectives within a group, and actively create common understanding, will do better.
To be sure, book-smart and stuff-smart IS important, but people-smart will take you farther than book-smart and stuff-smart just about every time.
Of course, read people like Steven Ceci or Robert Sternberg, and you might come to the conclusion that much of what we like to label as smart IS really people-smarts.