the old man appears, sticks a knife into his leg, and calls him the ‘Knife Prince.’ The boy now wants to set forth on his adventures… The knife in his leg is of vital importance: If he draws it out himself, he will live; if anybody else does so, he will die.
Jung reads the knife as an archetypal instrument of fate and identity simultaneously, gifted by the Wise Old Man figure and encoding both heroic vocation and mortal vulnerability.
, The Archetypes and the Collective Unconscious, 1959thesis