Symbols often reflect the desires motivating characters to act. For example, in "The Lord of the Rings," the ring reflects the greed consuming whoever covets it. Those who desire the ring either act on this desire themselves by chasing the ring or stir others to action destroying the ring. Tolkien conflates symbol and the thing it signifies by imbuing the ring with the very magical powers it symbolizes: not only does the ring represent greed, but it has the real power of invoking greed. These tensions instigate the great journey of and ensuing hunt for the ring.
Sometimes symbols represent lessons characters need to learn. To learn these lessons, characters have to go on a journey, whether physical or psychological. For example, in Harper Lee's "To Kill a Mockingbird," Scout's father Atticus tells her that killing mockingbirds is wrong because they never harm anyone, they are just different. This lesson is the crux of the novel. Tom Robinson, the black man falsely accused of rape, and Boo Radley, the reclusive neighbor ostracized by the community, are both mockingbirds around whom Lee orchestrates events to so that the protagonist Scout can learn to empathize with them.
In George Eliot's "Silas Marner," the protagonist obsesses over the pile of gold coins he has earned through weaving until they symbolize the meaning of life for Marner and become an extension of him. When the coins abruptly disappear, the direction of the story changes dramatically; Marner must find something new to live for and so adopts a child. The loss of one symbol forces the protagonist to adopt another, altering the rest of the events in the story, as the child Eppy becomes a major figure that influences the course of the plot.
Symbols can sometimes represent fears or problems characters have to overcome or are unable to overcome, resulting in a progression of plot or an ending to it. In George Orwell's "1984," rats represent a fear that the protagonist Winston must overcome in order to reunite with his beloved Julia and commit the ultimate rebellion against Big Brother. Because he is unable to face his fear, the story abruptly ends; the plot cannot continue without the protagonist overcoming this obstacle to action. The narrator has no more events to relate, because the story has cycled back to the beginning, a time of oppression, submission and hopelessness.