This work proposes a qualitative analysis of the particle-induced viscosity reduction phenomenon observed in polymeric composites like polylactic acid (PLA)/partially methylated silica particles, but not in composites like PLA/hydroxyl-terminated silica particles. The analysis is mainly based on considerations of the friction coefficients of spherical particles in the composites. The analysis reveals that sufficiently small particles, relatively weak polymer-particle interfacial interactions, particle rotation, and the existence of interfacial slipping in a polymeric composite are necessary conditions for the occurrence of particle-induced viscosity reduction, while long-distance particle-particle interactions based on polymer-particle interactions, and possibly existing additional interfacial elastic behaviors conversely lead to an increase in viscosity. The ratio of the radius of the particles to the gyration radius of the coils of polymer chains in polymer melts (R/R (g)) is found to be not crucial.