Knights of the Round Table pursued the Holy Grail in the legend of King Arthur. Indiana Jones and Dan Brown's people did the same. In the Titanic, they went after the 'Heart of the Ocean,' and Harry Potter's mission in the first book and film was to rescue the Philosopher's Stone. (Or Sorcerer's Stone.)

All heroes seem to chase something. Or someone. Luke Skywalker had to rescue the Princess Leia. Many of Sherlock Holme's cases were about chasing prizes like the Blue Carbuncle, the Naval Treaty or the Bruce-Partington Plans.

P. G. Wodehouse's Bertie Wooster was always trying to pinch stuff like cow-creamers, manuscripts or figurines.

All these prizes assume great importance to the characters of the above stories, but the point I want to make is that they are not that important to the reader or the movie-watcher.

For us readers or movie-watchers, avid for entertainment, the chase is more important than the prize. We are happy for the hero, of course, but we don't care if the prize is a naval treaty or a cow-creamer. We are more interested in the pursuit, for there lies the story, and the attainment of the trophy ends it. Romances end with hero getting his or her mate. Thrillers end with some priceless thing or kidnapped victim rescued. Or murderer caught. Whatever.

Sometimes the concept, this pursuit of the prize, is subverted or inverted. In the Lord of the Rings trilogy, everybody else seems to chase the ring, but the hero's mission is to lose it. In some thrillers, the hero is being chased.

Usually you will find that the prize is guarded by a dragon. HP and the Philosopher's Stone has a 3-headed dog on guard. Dragons are not literal dragons always, by the way. In a romance, it could be the girl's mother.

The basic concept of many stories is that the hero is asked to get the prize after defeating the dragon. The prize tempts and the dragon threatens. You will find the hero in early scenes or chapters in an undecided state, asking himself or herself if the prize is worth the risk.

Read my Why is Cinderella like the Titanic? hub if you haven't already.