Not really, if you know some history behind it.
You see, there were, before Episode I, a huge number of Sith. Their numbers grew and grew rapidly, building...strengthening
However, due to the size, there were many conflicts WITHIN the Sith ranks...Sith vs. Sith, that lead to the start of the demise of the Sith.
Later, a Sith by the name of Darth Bane made a new ruling for Sith...to prevent Sith in-fighting like there was when there were many Sith, there would only be two...a Master and an apprentice.
I'm sure that someone here could better flesh out the explaination. I just did that from memory from when I read the Episode I novelization.