This is lifted from the novel "Alamut" that the game writers used for inspiration. The novel is about a fictionalized version of the Ismaili, a Muslim group that were referred to as assassins by crusaders because they supposedly used a lot of hash (corruption on "Hashashin"). We don't know much about these original assassin's beliefs, because they operated out of a fortress that had its library burned once conquered and so we only know about them through their enemies. The assassins in the book were intended to be an allegorical portrayal of fascists with a very cynical, power hungry leader (this maxim is his own personal philosophy) brainwashing young men to have overwhelming obedience and carry out any violence the leader asked.