that's what really makes the story.

David refusing the king's armor, knowing it would just slow him down and make him unable to stay out of reach of that massive sword. I mean did he really take the field buck naked as his famous statue would imply? Probably not, but neither would he be in a stranger's clothes.

David having the skills to find the perfect ammo, and having the skills to execute a boom, headshot!

Goliath being stupid enough or blind enough to think he was being approached by David bearing "sticks", not a sling, even though his side would surely know what a slinger was.