There's a difference between futher investigation disproving a held model, and making a fallacy as "I went to Lourdes and Healed, therefore going to Lourdes heal people". That's why we use logic, to begin with.The problem is, of course, that ultimately all of our models are variations on this theme. No matter how much research one does, one can never actually see causation, and there is always a chance that further investigation will disprove a currently held model.
That's the point with Oracles. Once you are cryptic enough in your speech, anything can fit your prediction. When Nostradamus said "there shall be a war uppon the black land", you could bassically make it fit anywhere you want. A war on a black land can be a war on Ucrania (whose land is dark). Or a war in Africa (being a land of black people). It might be a war on Persian Gulf (becouse the oil is black). So it's quite easy for him to be right: almost any war that happen, you can twist it to fit into the prediction comortably well.In one old issue of Dragon, there was an article on gypsies that included a random "tarot card reading" generator. Despite the fact that the players knew it was random, there was enough coincidence inherent in the game to make them believe it might not be. Hence, superstition can play a role even for PCs.
Once Crasus went to the Oracle, before his war with Julius Caesar. The Oracle did say him: "if you both go to war, a great roman man will be defeated". Yeah. Go figure.
