Stability is a key statistical parameter widely used in multi-environment trials to assess the performance consistency of genotypes, particularly for grain yield. While often applied to easily phenotyped traits, their relevance for complex and labor-intensive traits remains limited. A fundamental question in plant breeding is whether the goal of a breeding program should be to develop broadly stable genotypes (mega-varieties) or genotypes specifically adapted to target population of environments (TPEs). Stability plays a critical role in selecting elite lines for varietal release and breeding advancement, yet its biological basis and genetic mechanisms, remain unknown. Moreover, the value of stability is often weighed against phenotypic plasticity, raising questions about which property better supports resilience and productivity under diverse conditions. This chapter explores the continuum of crop performance across varied environments, reasoning why certain genotypes exhibit greater stability while others display higher plasticity, and highlights emerging insights into the genetic underpinnings of these from recent research.