[Corwyn Celesil]

One thing everyone seems to have missed is the influence of Iluvatar on the Quest. Of course this is never mentioned in LoTR, but remember in the Silmarillion that when the Ainur marveled at all that they could see of Arda, Iluvatar reserved some things for himself, things that would surprise even the Ainur. I believe firmly that one of these things was the existence of Hobbits. No one knows where they came from, and no one knows the depths within them. Iluvatar created them, and Iluvatar reserved them for this hour of intense need. Elrond said this: "I think this task is appointed for you, Frodo; and that if you do not find a way, no one will. This is the hour of the Shire-folk, when they arise from their quiet fields to shake the towers and counsels of the great. Who of all the Wise could have foreseen it?" Who appointed the task? Iluvatar. I think he took a secret delight in surprising those who thought themselves Wise with his plan to use the weakest among them. No one would have chosen Frodo to do it . . . which was why he was chosen, and as he went forth in the Quest, new things were revealed, born and developed in him. If you look at Gandalf's words to Frodo at the beginning of FoTR, he says much the same thing: "It was the strangest event in the whole history of the Ring so far: Bilbo's arrival just at that time and putting his hand on it, blindly, in the dark. There was more than one power at work, Frodo. The Ring was trying to get back to its master. [ . . . ] It abandoned Gollum. Only to be picked up by the most unlikely person imaginable: Bilbo from the Shire! Behind that there was something else at work, beyond any design of the Ring-maker. I can put it no plainer than by saying that Bilbo was meant to find the Ring, and not by its maker. In which case you also were meant to have it." And somewhere he says he doesn't know why he chose Bilbo for the orignal adventure; he seemed to have been meant to.
My point is this: because Iluvatar chose Frodo, Frodo was the only one who could have done it. And even though he never actually did it, Iluvatar was still at work even in Gollum, who still had some part to play... and played it.