Edited sentence: After going through a general overview of western mystical philosophy Eco settles on one particular notion that is important - and that is Occam's Razor: the idea that, if there is more than one explanation for something, the simplest one is the most likely.For example, the suggestion that Adolf Hitler was secretly a Templar (or assassin or whichever anti-semitic secret society Eco quotes) and more lurid assertions about Nazi occultism are of course nonsense - the simpler explanation is that Hitler was a man angry about Germany's economic and political situation, and this rage caused him to write Mein Kampf - the Templars don't come into it.Interestingly, William of Baskerville, the central character of Eco's earlier novel The Name of the Rose, is based in part on William of Ockham, for whom the principle of Occam's Razor is named.The Plan is, of course, completely based on links that according to the Razor would be disregarded.This way of thinking is completely forgotten when The Plan takes over, and it takes the dying Diotallevi and Lia to bring Casaubon down to earth