In many cases, coworkers simply don't see or fully understand the scope of another's job. Some people are talented, but don't like to "toot their own horn", or maybe they are just so good at what they do, they make it all seem effortless.

However in the information technology profession in particular, there is untapped potential in almost every team member. Sometimes that potential may be even kept hidden by the individual themelves. For example, the girl who keeps to herself, avoiding high pressure assignments, punching in at 9am and out at 5pm, may have a gig on the side where she leverages technical skills that are outside the scope of how she's been typecast by coworkers on her day job. It would be in the best interest of the company to draw these people out, acknowledge them, and develope them to the fullest of their potential, before they get lured away by a competitor.

There is a book called "The Invisible Employee" by Gostick and Elton that every manager should read.