The mystical system of the Assassins was based upon a series of ritual initiations. In these initations the candidates were slowly taught the secrets of the sect while at the same time each one of the initiations proved that what the candidate had been led to believe as the supreme truth was in fact a lie. So in each subsequent initiation, the beliefs or teachings of the previous were destroyed.
This is another reason for attributing to the Old Man of the Moutains the phrase "Nothing is True, Everything is permitted", and this sort of belief and dis-belief is used in modern chaos schools where a particular belief structure is employed while it is useful only to crumble later. This ultimately leaves the initiate with a peculiar and singular view of the Universe.
As has been stated earlier the the name Assassin is derived from consumer of Hashish, and it has been rumoured that they were called this because of the use of Hashish in their ceremonies. While this is not unlikely it is also probably that the altitute alone would have produced the same dizzy euphoria and blood shot eyes accompanied with hashish use. This ecstatic trance or use of hashish in rituals would also have been similar to the rituals of other dervish or sufic sects at the same time.