Nothing is true; everything is permitted.
Yeah, it's from Assassin's Creed, but it's also thought to be the dying words of Hassan-i Sabbah, who led the actual assassins. It's more likely an embellishment than something he actually said, but it still has meaning. To me, it simply states that nothing and nobody, no matter how they're presented, is handing you the truth on a plate, just like that. No ultimate morality, no way things should be just because, no unbiased statement, and most importantly, no easy right answer that will make everything better and relieve you from having to think and question.
Of course, it's impossible to ever fully live up to it, and I do far worse at it than many...