I am Darth Revan, Dark Lord of the Sith.
Those who use the dark side are also bound to serve it. To understand this is to understand the underlying philosophy of the Sith.
The dark side offers power for power's sake. You must crave it. Covet it. You must seek power above all else, with no reservation or hesitation.
The Force will change you. It will transform you. Some fear this change. The teachings of the Jedi are focused on fighting and controlling this transformation. That is why those who serve the light are limited in what they accomplish.
True power can come only to those who embrace the transformation. There can be no compromise. Mercy, compassion, loyalty: all these things will prevent you from claiming what is rightfully yours. Those who follow the dark side must cast aside these conceits. Those who do not—those who try to walk the path of moderation—will fail, dragged down by their own weakness.
Those who accept the power of the dark side must also accept the challenge of holding on to it. By its very nature the dark side invites rivalry and strife. This is the greatest strength of the Sith: it culls the weak from our order. Yet this rivalry can also be our greatest weakness. The strong must be careful lest they be overwhelmed by the ambitions of those working beneath them in concert. Any master who instructs more than one apprentice in the ways of the dark side is a fool. In time, the apprentices will unite their strengths and overthrow the master. It is inevitable; axiomatic. That is why each master must have only one student.
This is also the reason there can only be one Dark Lord. The Sith must be ruled by a single leader: the very embodiment of the strength and power of the dark side. If the leader grows weak another must rise to seize the mantle. The strong rule; the weak are meant to serve. This is the way it must be.
My time here is ended. Take what I have taught you and use it well.