as told by
Sith Master Kell-Doqu
The Jedi would have you believe that their is a good and bad aspect to the Force, a Light and Dark Side. But we Sith know this to be a lie created to suppress their students from realizing their full potential. The true nature of the Force is neither Light nor Dark, it simply exists to provide balance within the universal chaos. The Light and Dark Sides are but aspects of the Force. The Jedi have always sought to show the barrier between the two, but it does not exist. The line blurs. All that can be relied upon then is the source of these two aspects, for it - the Force - depends on the existence of nothing, unlike the Light, which cannot exist without the Dark. The Force simply is.
However the term Dark Side and Dark Jedi has been accepted by us simply to distinguish us from them. Dark Jedi survive by stealth and secrecy, and therefore remain secluded in the shadows, or the darkness. Dark Jedi do not shun the Dark Side, we embrace it.
The question of whether Dark Jedi and Sith are synonymous is an ancient one. The reason for this is because the answer is both yes and no. A Dark Jedi is normally an individual who was trained by a Jedi and has decided that his master is too inept to properly train him in all aspects of the Force, or in another instance one who was trained solely by a Dark Jedi. A Sith, on the other hand, is one who has been indoctrinated in the ancient Sith techniques: alchemy, sorcery, genetic manipulation, etc. A being can be either Dark Jedi or Sith, or both.
The gray area exists when identifying one from the other. In the Sith of the current era (i.e. Imperial Entanglements) broadly include both types of Force users. Collectively they are all referred to as Sith. Usually individuals begin their training as Dark Jedi and become full Sith during their study as Adepts; however, it is possible for a student to learn only Sith abilities if that is all their master will teach them.
The Sith have endured for millennia, despite their apparent fall. In fact, we have always allowed the Jedi to believe that we have been destroyed. We allow them to forget while we remember. Our long endurance was made possible by the great Dark Lord of the Sith, Marka Ragnos. By establishing the first Sith Sanctuary and the laws for protecting it, he laid the foundation for an everlasting Sith presence in the galaxy.
Now there are hundreds of Sith Sanctuaries, ranging from small hidden temples in the midst of populace cities to vast fortresses on isolated worlds. All of these are protected by our laws; no Sith will reveal the location of a sanctuary to another and no Sith will retreat to a Sanctuary if pursued. Most Sith know nothing of the Sanctuaries to lessen the chance that they may reveal its location.
The Sith survive in solitude, most working alone or in small groups. A Sith in immediate danger will never seek the assistance of another Sith and as such a Sith will only rarely come to the aid of a comrade.
The Force provides great power and it commands even greater respect. Through the Force, a Sith can rule worlds, even galaxies. But one must not forget that nothing in this universe is free. The Force requires service in return for the power it provides. A Sith learns to bend the Force to his will, but it will extract its toll. Most often the body suffers, your muscle becomes weak and your bones brittle.
The Jedi, in their arrogance, believe that if they ask nothing of the Force then it asks nothing of them. This is far from true, Jedi grow old and wither, and sometimes live for centuries just as we Sith do, so long as the balance of service is maintained. If you allow the Force to work through you to achieve the natural order that it desires the price will be less than if you constantly bend the Force to your will.