A small boy of no account, typical of the area and time, made a difference. All the men were at war with a neighboring tribe. The feuding had been going on for some time with no let up in sight. These were the troubles of the times.
Reaching into his bag and taking out a stone, he slung it and struck the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground. (1 Samuel 17:49 NIV)
Never doubt! Never look at the circumstances.
There is a “David” in all of us.