Whenever I read LotR and reach the battle between Eowyn and the Witch-king, I get the impression that the reason why the prophecy loophole works isn’t that the Witch-king is unkillable except for some illogical weakness nobody had thought about yet for misogynistic reasons, but that the Witch-king himself derives so much of his power from the fear he instills in others and from his own belief that he is unkillable. Eowyn doesn’t fear him, because she doesn’t fear death. When she twists his words right back at him, she’s not trying to exploit a prophecy loophole, she’s just making a play on the double meaning of the word «man» with fairly standard battlefield bravado.
But, crucially, it gets the Witch-king wondering if there might be an actual loophole in the prophecy. He starts doubting his own invincibility. There’s no logical reason why a woman might be able to kill him if a man cannot, but prophecies are tricky things. What if …
And this is what undoes him, in the end. This last minute doubt. The Witch-king, deep down, believes that Eowyn can kill him, thus making it possible for her to do so.
A lot of tcomc adaptations I've seen have ended the story by having Edmond get his revenge and then happily reunite with Mercédés and leave the story like that, and here's why that does NOT fly with me.
The Count of Monte Cristo is NOT a love story about Edmond and Mercédés, though it starts that way. A lot of adaptations tend to do this, as in zero in on the romance (and leave Haydée out if the plot, wtf???) But the romance, although an accessory of the tragedy, is NOT central to the tragedy! Mondego, Danglars, Caderousse, and Villefort didn't JUST steal Edmond away from Mercédés, they also a) left his father to starve to death, b) took advantage of Mercédés' misery to marry her when she had no one left, c) abandoned Edmond to suffer in prison presumably for the rest of his life, and d) did all of that other insane shit that didn't affect Edmond personally.
But the point of the original ending is that there is too much time lost between Edmond and Mercédés, too much loneliness between them, and they have changed too much apart from each other for things to go back to how they were. Although Mercédés can see past the Counts callousness to find his old humanity, Edmond HAS changed, he's not the same bright-eyed young man who had so much in life to do. Mercédés isn't the same untroubled, poor woman Edmond fell for, and that's okay! They still love each other, though they have different paths in life and different responsibilities! It just seems, maybe cheap is the right word, to give Edmond the traditional "happy ending" by having him "get the girl back" in the end, as if that were the point of his efforts. They've earned their peace!