"At the moment of impact the hands work not together but against each other. The left hand must bear back against the right. Immediately prior to and during the moment of the club's contact with the ball, the right hand speeds up the club head. It cannot do this if the left hand fails to offer a backward resistance against the upper end of the club handle. This back pressure of the left hand must be exerted at the moment of impact." Original Golf Fundamentals, Dunns of Musselburgh, Scotland
DUNN of Musselburgh, Scotland (1922) says : "The reason why many players "slice" is because they either do not have strong hands or they fail to use their hand strength at the critical moment when the power of the stroke is to be transmitted to the ball.
The majority of players who fail in transmission of power do so because their left hand fails to act as a fulcrum for the right hand to strike against. The left hand has to bear back against the right.
To understand this matter, take a club in hand and press the face of it against any solid obstruction, with enough force to bend the shaft. Maintain this pressure and ask yourself, "What am I doing with the upper palm of my left hand?" You will discover that you are very decidedly pressing the club handle backward against the forward pressure of the right hand. This back pressure of the left hand must be done at the moment of impact if you are to overcome the resistance of the ball."
Download : "The left hand has to bear back against the right." Page 115 Dunns of Musselburgh, Scotland, 1922