A common distance killer
One of the fundamentals that is common to good players is generating enough power, in slightly varying degrees, to play the course effectively.
The first power element is the path of the hands and the club moving inward— around the body as opposed to upward— on the backswing.
Moving the hands and club on a circular arc stores potential energy, as compared to moving them straight back over the target line. This dynamic is evident in many sports, perhaps most clearly with goal kickers in football.
If the arms move out on the downswing, the swing gets steep and cuts across the ball, causing pulls and slices, and loss of distance.