BBAO: Recalling the Andy Reid model - NFC North Blog - ESPN. It's been mentioned in the comments that Ben McAdoo is following a similar path as Andy Reid did in the 1990s. From the NFC North Blog:

Andy Reid was an offensive lineman during his playing career and coached the Green Bay Packers' tight ends and offensive linemen for five years until then-coach Mike Holmgren switched him to quarterbacks. The move worked for the Packers, Reid and quarterback Brett Favre alike, and it's a model -- coincidental or otherwise -- that current Packers coach Mike McCarthy followed this winter.

I don't exactly know what makes a good coach. Great players don't often make great coaches. And forgettable players sometimes make great ones.

Another good example is Mike McCarthy's career path. After he played tight end in college at Baker University, he worked his way up through the coaching ranks to become a quarterbacks coach with the Chiefs and Packers. Then he became an offensive coordinator, and eventually a head coach. I don't expect the Chiefs thought after they hired him in 1993 to be their offensive quality control assistant that he'd one day become a top offensive mind and a Super Bowl winning head coach.