A Psychological Analysis of the Dark Side

I think that is one valid way to look at Vader's journey. But obviously Palpy's journey is a different one ... and presumably Plagueis's journey was different from either one of those.

"Sith are as varied as the cosmos, but they are all Sith."

-- from a Palpy fan fic I love (but can't link to on this board.)

I think the basic commonality all Sith have is the act of overlooking the pain they cause others. What differs among Sith is HOW they're doing this and WHY they're doing it.