Sith Failures

[Darth_Nihil]

Even though some Sith in the past have been very wise and powerful in their teachings is beyond doubt, the very reason why the Sith forces have been unsuccessful in exterminating the Jedi is because a lack of judgement has taken place. You all see, the problem is, the more powerful a Sith Lord gets in terms of combat prowess and use of the Force, the more complacent he/she will become. In some cases, they will sometimes get the idea that because they are so powerful in the Force, they think they have the power to take on any Jedi that they come across, therefore lacking sound judgement. IF they were as WISE as the True Sith of old, they would not make the mistake of thinking of themselves as all-powerful. Remember, everyone, never underestimate the Jedi.

[Tharan Mora]

Partially correct...
But the largest reason for Sith failure is that many were stupid in the past. The goal of personal power, ruthlessly gained, obviously necessitates sound judgement. For example, it's actually more beneficial to the individual to NOT attempt to seize power when the Sith Empire is collapsing.

To gain true power, the individual must take some steps to ensure that a seat of power remains to be taken.

[DarthBANE]

Hardly I disagree when bane came up with the rule of two it was not simply bc they were fools that had dark side hubris he saw that the weak would team up several to take down one leaving the ranks swelled with average instead of extraordinary...being the main reason he dealt with them by playing their hubris against them w the thought bomb