‘Quite correct,’ said Dumbledore, nodding. ‘But don’t you see, Harry, that if he intended the diary to be passed to, or planted on, some future Hogwarts student, he was being remarkably blase about that precious fragment of his soul concealed within it. The point of a Horcrux is, as Professor Slughorn explained, to keep part of the self hidden and safe, not to fling it into somebody else’s path and run the risk that they might destroy it — as indeed happened: that particular fragment of soul is no more; you saw to that.