He knows too much and must leave, albeit with a choice of parting gifts. He declines a magic sword and magic harp that would make him the greatest warrior or greatest bard and takes the massive "Book of Three", which "holds everything that was ever known, is known, and will be known".
He knows too much and must depart, even if he has a selection of farewell presents. He rejects a magic sword that would make him the greatest warrior or a magic harp that would make him the greatest bard and opts for the substantial "Book of Three", which contains all knowledge past, present, and future.