Since he heard the women’s praises from all over towns of Israel about David’s victory over tens of thousands, Saul became jealous of David. Since then, Saul always tried to kill David. Jealousy just led him to weariness. Saul forgot the essence that it’s for whom he did it—not how many he won over it—that matters. He should have done everything for nobody but God.
Then Saul was very angry, and the saying displeased him; and he said, "They have ascribed to David ten thousands, and to me they have ascribed only thousands. Now what more can he have but the kingdom?" (1 Samuel 18:8)