For an act to be voluntary, the agent need not know every muscular movement, pause, and downstream consequence. Selecting a purpose and acting toward it are central indicators of choice and acquisition.
A person intentionally goes for a walk, although many bodily processes remain beyond conscious inspection. The absence of such detail does not turn an ordinary walk into a reflex. An involuntary tremor, by contrast, lacks the same intentional relation.
Thus the argument about exhaustive knowledge should not be turned into a denial of choice. Its intended conclusion concerns the rejection of independent origination by the servant.