He crafted into it all of his passion and hope, and it all accumalated in the single moment he threw the knife. It WAS a work of dreams and hopes, and the only material that can actually be worked with in such a task is Dreamstone. Those hopes and dreams took the form of the three spirits, which form a Dreamstone based weapon when used. It can be a knife, a sword, a swallow, even an effing fork. (Imagine Quina Quen wielding the Mastermune).