In Of the Rings of Power and the Third Age, Elrond and Gandalf have a conversation:
Therefore naught was done at that time, though Elrond's heart misgave him, and he said to Mithrandir: 'Nonetheless I forbode that the One will yet be found, and then war will arise again, and in that war this Age will be ended. Indeed in a second darkness will it end, unless some strange chance deliver us that my eyes cannot see.'
'Many are the strange chances of the world,' said Mithrandir, 'and help shall oft come from the hands of the weak when the Wise falter.'
I can't figure out on what basis Gandalf is making this statement.
Of course, his statement is in the future tense, and this is exactly what happens in The Lord of the Rings. But it's not based on any precedent that I'm aware of, and if it's meant to be a prophecy, it seems like a rather audacious one.
The Silmarillion is the only work of Tolkien's that I'm at least passingly familiar with aside from The Lord of the Rings, and as far as I recall, it deals exclusively with the deeds of the strong, both wise and unwise. I can't recall any cases offhand where the Wise faltered and were saved by the weak.
Strong and weak are relative. Men are weaker than Elves, and all mortals are weaker than Morgoth and the Valar. Could this be what Gandalf meant by "weak"? If so, what incidents could he be referring to? Are there cases in his other writings where the weak help the faltering Wise?