The yield resistance of a coated sphere subjected to normal contact loading is studied based on a finite element analysis. Moderately hard coatings that were omitted in previous literature are considered. A maximum weakening/strengthening effect of minimizing/maximizing the yield resistance is observed to be linked to the transition of yield inception location. The necessary condition for a hard coating to strengthen a coated sphere is proposed. Only hard coatings with yield strength ratio above a threshold value can provide a constructive strengthening effect.