Motor variability occurs because there are always more elemental variables (muscles, joints, motor units, etc.) in the effector system, which creates the movement, then there are in the actual outcome of the movement. These elements are called degrees of freedom.
These degrees of freedom are also redundant.
We have redundant anatomical degrees of freedom. We have more muscles than needed to perform various actions, and these muscles can span multiple joints.¹
We have redundant kinematic degrees of freedom. An infinite combination of types, locations, directions, and quality of movements is present.¹
We have redundant neuromuscular degrees of freedom. There are multiple motor neurons synapsing on the same muscle as well as many instances of a single motor neuron synapsing multiple muscles.¹
It’s essentially impossible to count the number of degrees of freedom in the human body. This redundancy exists in every single biological object and mechanical concept previously discussed.