The wrist cock as a result of the folding right arm. As you take the club back the right arm folds pulling in the right hand. Since it's lower on the grip it causes the left wrist to hinge or cock at the wrist. Some people say the wrist cock naturally but it's really the result of mechanical action.

The best way to take the club back is with a right arm lift. From address lift the club straight to the top with your folding right arm. It swings your left arm back across your chest. When it connects it will pull your shoulders back. They will in turn pull your hips back. What you are doing in affect is turning the top of the spring against the bottom so you get a good coil. If you turn every thing together, the arms, shoulders and hips you're turning the whole spring and it doesn't have very much mechanical advantage.