You could say that Hela was the All-Father's first disappointment. Oh, she excelled in all manner of things, as he urged her to do, but he had raised a conqueror who knew no restraint.
When Hela failed to come to heel at the end of your grandfather's conquest of the realms, Odin handled the problem the way he tended to handle most unpleasant things. He locked her away and covered up all evidence that he'd ever had a daughter. In another genius move, he linked the bars of her cage to his lifeforce. No Odin, no prison. Do you see where this is going?