the.com/sword in the stone

means A test or symbol that reveals someone's destined right to a role by proving a worthiness that mere effort or force can't fake.

from Rooted in the Arthurian legend — first spun by medieval chroniclers and romance writers — in which the boy Arthur alone can pull a sword from an anvil-set stone (or in some tellings an altar), proving his right to be king not through conquest but through a kind of sanctioned fate. The tale drew on older Celtic and mythic motifs of magical weapons that choose their bearer. Over time the phrase broke free of the legend itself to mean any test designed to single out the one person truly meant for a role.