This paper addresses the question of failure in granular materials by considering the theoretical framework of the loss of sustainability. The physical meaning of this notion is developed, and expresses through a formalism developed in large strains. This formalism has given rise to a fundamental equation that relates the increase in the kinetic energy of a system to the second-order work. Then, restricting the discussion to homogeneous systems, the directional analysis is properly shown to be a convenient procedure to detect the occurrence of such failures.