The resolved shear stress in the direction of (101) is maximum and in the direction
of (121) is minimum on the {111} plane as the Schmid's factor is maximum along
(101) and minimum along (121) direction. Since the maximum and minimum
resolved shear stress occur along the (101) and (121) directions respectively, these
directions are a family of primary or 'easy slip' directions and secondary or 'hard
slip' directions, on the {111} plane.