Good forges burn hotter than lava, and dragonfire even hotter still, yet Gandalf said that the biggest, baddest dragon who ever lived Ancalagon the Black (who makes Smaug look like a whimpy little butterfly in comparison) wouldn't be able to harm the One Ring.

It's the magical tie to Orodruin/Mount Doom that allows for its destruction.

[–] threelonmusketeers@sh.itjust.works 2 points 12 hours ago

and dragonfire even hotter still, yet Gandalf said that the biggest, baddest dragon who ever lived Ancalagon the Black (who makes Smaug look like a whimpy little butterfly in comparison) wouldn't be able to harm the One Ring

I don't remember this. Where was this mentioned? Council of Elrond?