I made this little drawing to help someone get an idea of what is most important about the D Plane. This picture is basically showing a picture of a swing plane from down the line for a right hander. As I look down the plane, there is only one place on that line that is more right than any other.
This point would be low point. If the ball comes off the face any other place on that line, then that means that the club head is moving to the right until it reaches low point. So, if this swing planes low point is pointing toward the target, any ball hit before that assuming a centered hit and a square to target club face shape can not fly straight.
In other words, if you are looking at your swing on video and your club travels right on this line while it’s pointing directly at the target and your club face is pointing directly at the target but you hit the ball before the low point, you will not hit it straight. Please check out the other D Plane posts on the D Plane page above.