When you think about it, oaths, curses, prophecies, fate, etc have a really large hold in Tolkien's work that sometimes you wonder, where is free will? Of course it can easily be refuted by saying "Frodo chose to be Ring-bearer" and such, but when Gollum fell as he was dancing around and around, or the fate of Turin and Nienor, it really tickles your brain, in a fashion.
