Another wonderful life lesson that Dark Souls teaches us by shoving sharp, flaming instruments into our soft bodies is the concept of humility.
The thing about Dark Souls (specifically the PVP) is that regardless of how much of a hard ass you think you have become, the slightest fuck up can leave your corpse in a bloody heap on the ground. More often than not this is apparent in PVP. I find that no matter how many hours I may spend crafting the "perfect" build for PVP some guy will stroll up in my game and gut my character faster than I can say "Indicted". It is easy to disregard this as cheap or broken, but in reality you have just as many options as anyone else. There is no best build, strategy, or gear. You have to roll those dice and live with the outcome.
Dark Souls will never miss a chance to press its boots deeper into your throat just to remind you that you are not in charge. It is simply allowing you to play in its world until it has had enough of you. These are the terms you agree to when picking up your controller. You may be the best, but not always.
It's important to remember this in all aspects of life. It's okay to fail, it's okay to not be the best and it's perfectly acceptable to not be perfect.
Your effort and willingness to overcome far outweigh your mistakes.
Every detail in the Dark Souls world has been placed with care. Each item placement, each enemy, each environmental hazard tells a story as long as you take the time to read it.
For example you are able to find a weapon, a mace, just before you stumble into an area full of blood letting skeletons that will decimate you if you stumble into their domain too early. Which is very likely because its two feet from the "Hub" area of the game.
Why is this important? Crushing weapons such as maces, and clubs will knock the skeletons to pieces with certain attacks! Swords and piercing weapons do not have this effect. The game never tells you this. A tutorial never pops up to tell you "Hey that mace you got is good for smacking skeletons!". Instead it just provides you with tools and leaves you to use them as you see fit.
This is even more apparent when trying to decipher the story Dark Souls has hidden in its world. Item descriptions, item placement, and everything else mentioned above describes every happening in the twisting plot.
Never take things for face value. Examine everything. Question everything. Experience everything.