Wharton management professor Ethan Mollick has a message for knowledge-based companies: Pay closer attention to your middle managers. They may have a greater impact on company performance than almost any other part of the organization. In other words, says Mollick, “the often overlooked and sometimes-maligned middle managers matter. They are not interchangeable parts in an organization.” His view upends the long-held belief that performance differences between firms are due mainly to organizational factors – such as business strategy, management systems and HR practices — rather than to differences among employees.…