Electrocatalysts　support　crucial　industrial　processes　and　emerging　decarbonization　technologies,　but　their　design　is　hindered　by　structural　and　compositional　changes　during　operation,　especially　at　application-relevant　current　densities.　Here　we　use　operando　X-ray　spectroscopy　and　modelling　to　track,　and　eventually　direct,　the　reconstruction　of　iron　sulfides　and　oxides　for　the　oxygen　evolution　reaction.　We　show　that　inappropriate　activation　protocols　lead　to　uncontrollable　Fe　oxidation　and　irreversible　catalyst　degradation,　compromising　stability　and　reliability　and　precluding　predictive　design.　Based　on　these,　we　develop　activation　programming　strategies　that,　considering　the　thermodynamics　and　kinetics　of　surface　reconstruction,　offer　control　over　precatalyst　oxidation.　This　enables　reliable　predictions　and　the　design　of　active　and　stable　electrocatalysts.　In　a　NixFe1-xS2　model　system,　this　leads　to　a　threefold　improvement　in　durability　after　programmed　activation,　with　a　cell　degradation　rate　of　0.12　mV　h-1　over　550　h　(standard　operation:　0.29　mV　h-1,　constrained　to　200　h),　in　an　anion　exchange　membrane　water　electrolyser　operating　at　1　A　cm-2.　This　work　bridges　predictive　modelling　and　experimental　design,　improving　the　electrocatalyst　reliability　for　industrial　water　electrolysis　and　beyond　at　high　current　densities.