What Was That Story About An Unbreakable Shield And A Spear That Can Break Any Shield?

I’ve heard the story in Phoenix Wright (1st game, 5th case), and in Pokemon Brock used that as a comparison to what watching a battle between a Rampardos (spear) and Bastiodon (shield) is like.
Could someone tell me the story, and what the solution and moral was in detailed and easy to understand words?