David has no choice but to flee from Saul, so Saul loses his best military leader. Saul鈥檚 actions damage his relationship with his son and in the chapters that follow, Saul spends so much time trying to kill David that he becomes ineffective at defending Israel against its enemies. Saul turns against those who could have been his most powerful helpers - God and David - and instead becomes his own worst enemy.
How different this story could have looked had Saul embraced God鈥檚 plan. We could avoid a lot of stress and disappointment in life if we did things God鈥檚 way instead of developing solutions based on our inadequate efforts.