When dry ganular matter is tilted beyond a critical angle θc, grains start to flow until a state is reached where the slope of the surface is smaller than θc. In dry granulates this relaxation preferentially involves surface fluxes. In contrast wet granulates yield in the bulk. We uncover the origin of this behaviour by focusing on the structure of the balance equations of the forces, rather than applying a continuum model. The predictive power of the approach is demonstrated by a parameter-free prediction of the yielding of 2D packings with thermal motion and mass disorder.