Jedi Vs. Sith

[Silko]

Jedi.

In all manner of speaking, the Sith simply can't build a lasting foundation. They shoot themselves in the ass by killing each other off, and when they do come up with a brilliant plan for an anti-son of the bitch machine for the Jedi they never finish the job.

~Kuhblam

This is why Darth Bane created the Rule of Two. Bane realized that the Sith can not function as a system like the Jedi. The many will defeat the Strong and create a vacuum that the weak will kill each other to fill. Remember Palp was a follower of the Rule of Two. After a 1000 years of training and planning the Sith did defeat the Jedi. Two Sith where able to defeat the entire Jedi Order.