Kinda cringe for an origin of a creed, but it's a good rallying phrase. Surprisingly succinct.
"To say that nothing is true, is to realize that the foundations of society are fragile, and that we must be the shepherds of our own civilization. To say that everything is permitted, is to understand that we are the architects of our actions, and that we must live with their consequences, whether glorious or tragic."
Are there any similar phrases you've seen popularized by a game?
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.
The phrase was also supposedly the final words of Hassan i Sabah. Alamut is on my TBR, although I was apprehensive about a piece of work on the assassins that wasn't by a middle eastern author. Looks like it's interesting.