For decades, computational electrocatalysis has predominantly relied on static, idealised surface models. However, the physical reality of the solid-liquid interface is starkly different: under actual electrochemical conditions, the applied potential and local reaction environment drive continuous, dynamic catalyst reconstruction. In this work, we employ first-principles computational modelling to investigate the fundamental thermodynamic forces governing these operando structural evolutions. First, for pure transition metals, we demonstrate how the applied electrode potential fundamentally alters the surface free energy landscape. This potential-induced shift dictates the relative stability of various crystallographic facets, dynamically reshaping the macroscopic morphology and facet distribution under operating conditions. Second, we extend this physical picture to complex alloy systems, where the local reaction environment exerts a profound influence. Atomic-scale calculations reveal that the disparate binding affinities of reaction intermediates to different constituent metals provide a formidable thermodynamic driving force. This adsorbate-directed segregation overrides bulk stoichiometry, restructuring the surface and dynamically generating new active site motifs during reactions such as anodic oxidation. Ultimately, explicitly modelling these environment-induced structural evolutions is essential to move beyond static approximations. By integrating these dynamic phenomena into our theoretical framework, we bridge the gap between idealised models and the physical reality of the solid-liquid interface.