Why does Arthur fight Mordred after Gawain warned him?

Arthur fights Mordred despite Gawain's warning because he feels compelled to uphold his duty as king and defend his realm. Gawain’s warning highlights the potential for betrayal, but Arthur's sense of honor and loyalty to his knights drives him to confront Mordred, who represents a threat to his kingdom. Ultimately, Arthur believes that failing to act against Mordred would undermine his authority and the values of chivalry he stands for. This clash reflects the tragic inevitability of fate and the consequences of conflict among kin.