Gandalf Vs. The Witch King

Originally Posted by Raynor

Why? Sauron himself was previously defeated when he fought against two non-maiar (and Fingolfin wounded even Melkor). There is no single circumstance that I know of when a body is made invulnerable.

How exactly did they manage it? Was it down to a mixture of fate & luck, or through the power in them? There would be no luck or even fate involved if Gandalf fought the Witch King - it would like drawing fire against fire.