Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO3-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xZr5x/4]O3 lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.