Reconfigurable intelligent surfaces (RISs) are emerging as a transformative technology capable of shaping the wireless communications channel for favorable propagation. By passively beamforming wireless signals in the desired directions, RISs hold great potential to enhance network coverage and reliability of wireless channels. Nevertheless, several unaddressed challenges hinder its practical deployment in the cellular context. This paper identifies six pivotal challenges that must be resolved to ensure the successful integration of RISs into wireless communication networks. Further, we analyze the influence of different frequency regimes on the severity of these challenges. Finally, we highlight conditions under which RISs can deliver substantial benefits and stand out as a key enabler for next-generation wireless communications networks.