"Thank you Lord, that You are teaching me how to walk in total dependence upon You, for I know therein lies my greatest blessing." A Book Of Prayer, Stormie Omartian
David ran towards Goliath convinced he would over come his opponent. Goliath was a well armed giant and a trained soldier. David was a boy with only a small sling and no armor and no experience on the battlefield what so ever. This was an impossible match and yet David brought Goliath down, cut off his head, and took his sword as a trophy.
To me the key that unlocks this weird mystery is David's complete trust in God's ability to save him. David had never been on the battle field but he had been in the rocky pastures leading and watching over his flock. He had been through small battles with wild animals to save his sheep. He also had plenty of time alone to think and listen. David ran towards the giant that day armed in a relationship with God. This gave him all the courage he needed for his victory.