The Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives browned food its desirable flavor.
The biggest enemy of browning is excess moisture. Water boils at 100°C (212°F), whereas the Maillard reaction occurs rapidly between 140°C and 165°C (280°F to 330°F). If your protein is wet, the heat energy goes into evaporating surface water instead of browning.
Always pat proteins dry with paper towels before searing, preheat heavy pans, and avoid overcrowding the pan to maintain high thermal mass.