Scio Occultus Res
Like Atlantis, the Holy Grail is more a code-word for an idea than it is an actual object. In mage society, the Holy Grail is the lost secret that will heal the world. Each mage has a different idea of what it might be – perhaps it really is the Cup of Christ, or the Peaches of Immortality, or the Mason Word, or (as the Bonehunters believe) the re-establishment of Atlantis and the assault on the Supernal World strongholds of the Exarchs.
Whatever the specific idea a person holds, the idea of the Holy Grail has become the universal referent for the concept.