Reincarnation and Prophecy
Of course, it was entirely possible that the Beggar Sage possessed a mind that exceeded even that of his own. While Rui had yet to come across anyone who was clearly superior to him in this regard, he did not think that he was the greatest that the Panama Continent had ever seen.
Partially because it was embarrassingly arrogant to think that his mind was the greatest to grace this world.
Aside from that, he especially was not too skeptical because of the revelations that human sages were effectively immortals that could seem to be able to undo death or reincarnate.
He knew reincarnation was possible.
He had gone through it himself, after all.
Furthermore, it was the reason that his mind was as powerful as it was. While he had been exceptionally bright even in his previous life, the growth that he gained through this life was unlike anything he had ever experienced.