The Lord of the Rings trilogy is an anarcho-nihilist text, in which the righteousness of resistance is not measured by the success of that resistance but rather by how exhaustively those resisting do so. Frodo fails; he falls to the ring's influence and at the last moment of his journey he succumbs to the forces of authoritarianism. But he is none the less a hero, because he did all that he could: we know that he failed not because he balked, but because he had no more to give. Tolkien's ultimate answer is that in some cases only divine providence might carry the day, but the heroes of his story do not carry out resistance with the knowledge that divine providence will come or with the knowledge that there is certain hope for the future, they can only struggle even in the face of doom.
Moreover, the wisest inhabitants of Middle Earth are arguably the elves, and they know with certainty that they are ultimately doomed. Their way of life will end, magic will fade from the world, and all they have fought for will depart like mist beneath the rising sun. The most learned of the elves literally know that they can't achieve more than temporarily slowing the inevitable disappearance of everything they hold dear. And none the less, many elves choose to resist.
Time and again, Tolkien presents us with a story in which it is resistance itself that's noble, without regard for outcome.