Essentially, in Norse mythology, all events are inevitable because they have already happened and are eternally happening. A wyrd or fate is not an inalterable future, so much as a part of the present we have not yet experienced. It's a tremendously fatalistic worldview, it's true, and so inimical to modern American culture that it's rare to see it done well in English-langage fantasy, or even touched upon--acknowledged--at all.
Greg does a great job with it, and that delighted me, and I meant to mention it before.
What's also tremendously cool about Norse myth is the way things are both symbolically and literally their names. So Thor (as an example) can be an individual--the god of thunder, who carries a hammer which strikes like a thunderbolt (which IS, in fact, a thunderbolt, Mjollnir that smashes...); and he can also symbolically be the god of thunder, a personification of random violence and flash-fire temper; but he is also, all at the same time, quite literally, thunder in his own person.
Anyway, it's really really cool.