<p>The stability of jointed rock slopes is critical for the sustainability and resiliency of civil infrastructure and communities. Complex interactions between the natural fracture (NF) network, the rock matrix solid rock blocks, and boundary conditions govern the mechanical behavior of slopes. Environmental stressors, including weathering, degrade the mechanical properties of the rock matrix and NFs, which will lead to progressive failure of the entire slope. The conventional numerical analysis of slope stability, a.k.a., strength reduction method assumes that only shear strength parameters (cohesion and friction) of the rock mass degrade to the same extent in all rock mass components (NFs and the rock matrix). This study shows that the conventional approach overestimates the factor of safety (<i>F</i>.<i>S</i>.) against failure and underestimates the consequences of failure (e.g., runout distance, displaced volume, and runoff velocity). All strength parameters, including cohesion, friction, tensile strength, and fracture toughness, must degrade, but there is no data on the extent and rate of those reductions compared to one another and those for the rock matrix and NFs. We also show that the NFs and the rock matrix contribute to different extents to the stability of the jointed rock slope, and the difference depends on the internal structure of the rock mass.</p>