On superstars..........................Part the first

     The first thing the researchers noticed, as they began crawling through all that data, was that the firm's most productive workers, its superstars, shared a number of traits.  The first was they tended to work on only five projects at once - a healthy load, but not extraordinary.  There were other employees who handled ten or twelve projects at a time.  But those employees had a lower profit margin than the superstars, who were more careful about how they invested their time.
     The economists figured the superstars were pickier because they were seeking out assignments that were similar to previous work they had done.  Conventional wisdom holds that productivity rises when people do the same kind of tasks over and over.  Repetition makes us faster and more efficient because we don't have to learn fresh skills with each assignment.  But as the economists looked more closely, they found the opposite.  The superstars weren't choosing tasks that leveraged existing skills.  Instead, they were signing up for projects that required them to seek out new colleagues and demanded new abilities.  That's why the superstars worked on only five projects at a time.  Meeting new people and learning new skills takes a lot of additional hours.

-Charles Duhigg,  Smarter Faster Better:  The Secrets of Being Productive in Life and Business