First when looking to understand the shadow side you must look at the dark and light sides. The dark and light sides are constantly at war with each other over supremacy, there is a reason for this and I will get to it in a moment. The Shadow side has no conflict it is in balance with itself.
The reason the dark and light sides are at war is because they both are created by ambition. The ambition causes them to need a counter balance, according to the scientific law for every reaction there is an equal and opposite reaction. Therefore the only way they can exist is to balance each other out, some people call this a symbiotic relationship, meaning they benefit from each other, however in this case that is not an exact definition because they not only benefit from one another but are completely dependent on one another.
The Shadow side on the other hand is completely independent from the other two sides of the force. It does not need them to survive and in fact they are a hindrance to the shadow side, keeping it from achieving its full potential. The Shadow side has its own balance of good and evil and therefore does not need a counterpart. The shadow side is where the force flows most freely, because there is no conflict in the force. If you think about it, There are only two ways to exist in the force. The mutual existance of the light and dark side, which consequently is where most people are. The other would be the balanced existance of the shadow side as we call it.
People in the shadow side often have the most fulfilling lives because 1: there is no conflict and 2: You fully appreciate both aspects of the force because you live through both of them. Of course there are many trains of thought on the subject. I hope this first lecture was Insightful and helped give all force users a better grasp on the philosophies of the Shadow side. Thank you for your patience and may the force be with you.