system
Given the following post, respond as if you're commenting on Reddit:
human
If the Witch King can't be defeated or killed by a mortal man, how was he ever defeated in battle?

There were times where he was defeated and had to retreat, but why bother if he was so powerful? Couldn't he lay waste to whole armies himself?

LORD OF THE RINGS.
gpt
His line to Eowyn is merely a boast. That idea comes from a prophecy by the Elf Glorfindel stating that "Not by the hand of man" will he fall.  Now this is simply a prophecy of what *will* happen not what *must* happen.  The Witch-King is in no way immune to attack, especially from powerful persons like Glorfindel or Gandalf or even a Man like Aragorn.   What his true undoing was is the sword Merry stabbed him with. That Barrow-blade was designed specifically to fight the Nazgul.

Edit: Also the Nazgul have physical bodies, they are just invisible. They are much different than the ghosts from the Paths of the Dead who cannot wield physical weapons.