I don't mean to invoke this simply because the game is from a Japanese company (indeed, the game is built more around "Western" RPG principles,) but I think taking this attitude has improved my play and made the game more enjoyable and less stressful. Essentially, you just accept that sometimes, you're going to die, and sometimes that means losing Souls and Humanity you've collected. It encourages you to spend that stuff quick before you lose it, but also allows you to get used to reacting calmly to things in effective ways. While I haven't beaten them yet, I made some very nice progress on the twin Gargoyles fight (the first really major boss fight, as I understand) thanks to a kind of calm way of playing the game. In Dark Souls, if you're the inexperienced novice player like me, you're going to die lots of times, which can be frustrating at first, but soon you'll recognize these moments as times when the game is simply teaching you the layout of each room, which enemies to look out for and how to approach them.
The thing is, the player character is literally dead - well, undead. Let's get into the lore here. I'm only going from what I have so far in-game, and this is in pretty broad strokes.
The opening cinematic shows us that the world used to be ruled over by the Everlasting Dragons and was filled with Grey Trees. Deep below the world, however, there was fire, and the beings within the fiery underworld found Lord Souls, which gave them the power or animation to affect the world above.
What I find really interesting about this is that the dichotomy of good and evil or life and death doesn't seem to be the central conflict here. Nito, first of the dead, is pretty terrifying-looking, and definitely seems to skew more toward the evil side of the spectrum. The Witch of Izulath might have started out good, but birthed demons. But among them is also Lord Gwyn, who is your classic patriarchal deity, associated with order and sunlight, and someone who would typically be considered good.
They bring war to the dragons - Gwyn uses his lightning bolts to blast off their scales (the protective armor that keeps the dragons immortal) while Nito descends upon the with pestilence to kill them and the Witch burns the trees.
What the Lords do by defeating the Dragons seems less of a triumph of good over evil, but one of transformation and change over stasis. The dragons are "everlasting" and don't really seem to be doing anything except existing perpetually, but the people associated with fire are all part of a continuum of change. It's not life over death, but life and death over neither.
Skipping ahead to some spoilers, I know that Lord Gwyn is the final boss of the game - not that he's really a bad guy, but because he has "gone hollow" after fueling the flames of the world with his own soul for so long. I believe there are two endings - either you take his place or you allow the flames to die down and bring about an age of darkness.
What I see here is a kind of conundrum - were the Lords right to defeat the dragons? On one hand, by introducing the transitions of time, you introduce the inevitability of greater entropy. It's a physical fact that entropy increases over time - simply by doing things, we are hastening the Heat Death of the Universe, when all matter basically breaks down into a kind of even, disordered energy. That gradually burning out - consuming the fuel of the universe - is the consequence of the Lords' actions. But on the other hand, if they had not done what they did, the universe would be still and unchanging - just Everlasting Dragons forever and ever, locked into that state. Neither is really that appealing, to be honest, but this game doesn't seem like a very optimistic one.
The fourth Lord is called the Furtive Pygmy, and seems to be the progenitor of all humanity. There are some aspects of this part of the lore that I don't even have a theory about, including the way that Souls differ from Humanity, and how Humanity might be fragments of the eponymous Dark Soul.
But what I can speculate on is the Darksign. The Darksign is key to the game, as it's the thing that brings about your adventure and also, conveniently, provides a mechanical basis for why you keep coming back to life after you die.
Every character in Dark Souls, as far as I know, is Undead. People marked by the Darksign simply start coming back to life after they die. For a time, they retain their personality and intellect - their "humanity" (though I don't know how I should read into that.) But eventually, Undead go "Hollow," becoming the kind of mindless zombies you usually think of when you think about the Undead. The majority of enemies you face in the game (at least so far for me) are Hollows.
My take on this is that the Darksign seems to be putting humans into a state where they are reverting to the time of the Everlasting Dragons and the Grey Trees (skipping way ahead, there's some stuff in the upcoming Dark Souls III where there are Hollow bodies put into trees - which seems to back up this idea.) Without the light and dark of Souls and Humanity (that's a reach, but stay with me,) the Hollows revert to the kind of grey stasis that the Dragons presided over.
In a sense, because we're at this stage in the Dark Souls universe where the world's animating flame is burning down to embers, the transformation wrought by the Lords in that earliest age is now being undone, with the Undead being a symptom of this blurring between life and death. The Heat Death is happening, with the fires consuming their fuels, and the perhaps-ironic result is that it's all kind of becoming what it once was.
So that's what I've got so far. I know this is a game (series) with a rabid fandom, and that it's designed specifically to be open to interpretation. And I'm having a ton of fun speculating on the lore while my ass gets handed to me by all manner of just mean, mean enemies.