In the story Peradur in the Mabinogion, Peradur is told by his Uncle not to ask questions if he sees anything strange, unless someone explains the strange thing to him.
Leave, then, the habits and the discourse of thy mother, and I will be thy teacher; and I will raise thee to the rank of knight from this time forward. And thus do thou. If thou seest aught to cause thee wonder, ask not the meaning of it; if no one has the courtesy to inform thee, the reproach will not fall upon thee, but upon me that am thy teacher.
Later, Peradur sees a spear dripping with blood, and, taking his uncle's advice, does not ask about it:
he beheld two youths enter the hall, and proceed up to the chamber, bearing a spear of mighty size, with three streams of blood flowing from the point to the ground. And when all the company saw this, they began wailing and lamenting. But for all that, the man did not break off his discourse with Peredur. And as he did not tell Peredur the meaning of what he saw, he forbore to ask him concerning it. And when the clamour had a little subsided, behold two maidens entered, with a large salver between them, in which was a man's head, surrounded by a profusion of blood. And thereupon the company of the court made so great an outcry, that it was irksome to be in the same hall with them. But at length they were silent. And when time was that they should sleep, Peredur was brought into a fair chamber.
Later, he is told that his failure to do so meant the King would remain injured, and that he could have healed the king by asking about the spear.
And she greeted Arthur and all his household except Peredur. And to Peredur she spoke harsh and angry words. "Peredur, I greet thee not, seeing that thou dost not merit it. Blind was fate in giving thee fame and favour. When thou wast in the Court of the Lame King, and didst see there the youth bearing the streaming spear, from the points of which were drops of blood flowing in streams, even to the hand of the youth, and many other wonders likewise, thou didst not inquire their meaning nor their cause. Hadst thou done so, the King would have been restored to health, and his dominions to peace. Whereas from henceforth, he will have to endure battles and conflicts, and his knights will perish, and wives will be widowed, and maidens will be left portionless, and all this is because of thee."
Huh? Can someone explain why is it asking about the spear would have healed Peradur's family, and why he was originally told not to ask about the spear?