Let’s go back in time and talk to some golfers that are playing golf in the 1930’s and 40’s.  Let’s ask them what makes the ball curve.  What kind of answers to you think we would hear?  No internet, no d-plane talk and no high speed video or trackman.  What would they say?

Let’s think of some advances that might give us a clue.  In the late 1800’s, there was a change starting to take place from long nosed wooden heads to smaller and thicker wooden heads.  A new kind of driver was created that has a curved shape face.  Why in the world would they put a curve in the driver face that points away from the target vs. one that was curved to point the edges toward the middle.  This curve, or bulge, would lead to clubs name as a bulger.

They had noticed that shots struck on the ends of the club put a spin on the ball.  Toe shots added hook spin and heel shots added fade spin.  This spin was enough that it would curve a ball significantly away from the target even if the face was square.  By putting a slight curve in the face, so the toe pointed right of target and the heel pointed left of target, they found that the ball would end up closer to the target.
Effect of bulge
They did this because they saw the ball would start farther right before the hook spin from a toe hit brought it back.  The ball started farther right because of the shape of the face.  Over 100 hundred years ago they figured out that the shape of the face controlled it’s initial direction.

I think most golfers of the 30’s and 40’s era would say face first.  90% of the people I asked that know nothing about golf think that the face shape would control it.  I remember arguing at my PGA Checkpoint. I noticed when trying to curve the ball around the tree that I couldn’t aim the face behind the tree. I kept hitting the tree.

Is the d-plane earth shattering? No way.  It only helps with understanding what causes what.