I was reading a piece about the NE Pats. It was highlighting the fact that Belichek and other keys on that staff do not have pro playing experiences. That often a pro player, especially a successful player, moving into the coaching ranks sometimes thinks they have all the answers. Whereas guys like Belichek often search far and wide for solutions.
Bill Parcells too...no pro playing experience, Bill Walsh, John Madden, Don Mathews, Chris Jones either, Trestman never made it past TC I don't believe. There are many more.
Of course lots of ex players make great coaches. But maybe playing experience is not as significant as some of us think.