Lloyd Alexander's Prydain Chronicles make good use of theme, and one of the ways Alexander expresses his theme is with mirroring characters. In The Black Cauldron (my favorite in the series) Taran has two mirror characters: Adaon and Ellidyr. (Fair warning; if you haven't read the book and don't want any spoilers, you may not want to read this post.)
Adaon, son of the chief bard of Prydain, is everything Taran wants to be; kind, wise, brave and honorable, all without seeming to struggle for it. Actually, he is a lot like what Taran eventually becomes by the end of The High King.
Taran soon realized there was little Adaon had not seen and done. He had sailed far beyond the Isle of Mona, even to the northern sea; he had worked at the potter's wheel, cast nets with the fisherfolk, woven cloth at the looms of the cottagers; and, like Taran, labored over the glowing forge.
Pottery and weaving are two of the skills Taran learns in Taran Wanderer, and he sails to Mona in The Castle of Llyr. At this point in The Black Cauldron, Taran lacks Adaon's experience. Most of all, Taran lacks Adaon's understanding that true honor does not depend on having your deeds recognized.
Ellydyr, on the other hand, is an echo of where Taran is at the start of The Black Cauldron. Ellidyr is near Taran's age, and even more proud and impulsive. He, like Taran, is desperately seeking recognition -and confusing public recognition with honor. Ellidyr, the youngest son of an impoverished noble, is obsessed with rank (as is Taran the Assistant Pig-Keeper, so named because at least that way he'll have a title even if it's only one Coll invented for him.) Unlike Taran, Ellidyr is so consumed by his desire for `honor' that he is willing to act unscrupulously to get the public notice he thinks he deserves. He is a warning of what Taran could become if he continues to think of honor as dependent on how others view him, rather than dependent on his own actions.
With the characters of Adaon and Ellidyr, Lloyd Alexander is able to clearly illustrate the choice Taran is making about the man he wants to become. He shows us where each of those paths lead. I don't think its a coincidence that both Adaon and Ellidyr die over the course of the story, or that Ellidyr sees what he has become before the end. Alexander shows where the roads go completely, including their end.