What is the search for the Holy Grail and how is it like the story?

The
search for the Holy Grail is usually referring to the quest for the Goblet that Jesus drank from
during The Last Supper, which if you find and drink from, will bring you eternal life. Certain
twists have been made on this concept, such as can be seen in The DaVinci Code.
Metaphorically, the search for the Holy Grail is the ultimate search, the impossible
search, the hunt for something...