Ethos is self-belief. Self-belief is ignoring all those little lies that make mundane society work in favour of knowing what you personally want. Society says: "Money makes me happy." Society says: "It was just a one-night stand." Does money really make you happy, or does it just let you buy stuff that you don't really want or need to stop you thinking about how little you do with your life? Was she just a one-night stand because you were drunk and horny, or because you could never love a girl like you loved Jenny, when she was alive?
Self-belief is cutting through the bullshit and excuses and finding out who you are, down at your very core. It's not always pretty, but it frees your brain up for contact with the magical field surrounding the planet. It’s the hardest thing anyone can do, but it's also the most rewarding.
While it’s rated in numbers, the Ethos Attribute is mostly shorthand for your character’s beliefs. There’s not much point in having strong beliefs without ever knowing what they are. Ethos is a link between your character’s list of Beliefs and mechanical constructs like Conviction and Degeneration.
Beliefs are used in the game to help judge your character’s actions. Beliefs on the character sheet don’t have to colour everything she does, but standing up for a higher goal in the face of adversity is a core conflict in Æternal Legends. To that end, Legends can spend Conviction to help them achieve those goals.
The Light isn't a higher calling – it's all higher callings. Lightsiders live by the rule that conviction is magic, and that denying themselves that conviction in times of stress is “selling out.” Some follow the Light because they can't imagine a better way. Others came dangerously close to slipping to the Dark at some point in their lives and seek redemption with particular zeal.
A Lightsider has to live with the consequences of his convictions, so he doesn’t indulge his more unsavoury beliefs too often. He must be true to himself no matter what, because he’s forging a personal path to apotheosis from his beliefs. He must be careful to plan his path, directing his immediate urges to a more constructive goal. If he indulges himself all the time, he sacrifices the big picture for short-term satisfaction, but if he ignores what he cares about, he can’t take that next step.
While he must respect the bigger picture, no Lightsider can go for long without testing his beliefs. If he goes without for too long, he gets complacent. That stops him traversing the Spheres or advancing in his own Sphere.
Darksiders don’t test their beliefs. Self-awareness lets them know when they’re putting their own survival (or convenience) above their spiritual needs. Some Legends reach the Dark by a singular personal disaster; others find themselves unable to live up to the requirements of the Light.
Darksiders walk the Shells: the empty mockeries of the Spheres of Light. They advance by obliterating their beliefs. They surrender hope for the sake of quick power. They give up the Source within them and give the imprisoned Gods more power – power that they might use to escape their prison. And beyond even the Gods, the Dark Lord Da’ath provides the template for all Darksiders, who transform themselves into his avatars when they reach the pinnacle of power.
Save for Legends, all Aware – even those of the Dull Clades – are followers of the Light on some level. If they were not, they would either cease to exist or would never reach Awareness. Legends gain power through idealism and cynicism alike, but a life among the Unaware is the only thing awaiting those Aware who deny their inner calling.
Some of the Aware choose one side or another because their beliefs fit the vision of the faction provided by a charismatic Legend. A larger number don’t consciously care about the Light or Dark. They believe in nothing other than the heroism of a particular Legend, if that. Gangs of dwarves, gnome artists, and goblin sneak-thieves depend on their beliefs to remain Aware, but do so without any pretence of a particular alignment. And even if they follow the Dark, they don’t commit so strongly that it would compromise Awareness itself.