Jedi's who are ruling the muther-phkin galaxy not realizing that one who will "bring balance to the force" would knock them down because at that time - it was out of balance - the GOOD side was winning!
Not sure where this became a bad plot device. I think the biggest problem with the original trilogy was that the Jedi were made out to be intellectually infallible (Obi Wan and Yoda), and the best (only good?) part of the new trilogy was the realization of the concept that the Jedi were a diverse group of sentient life forms, some of whom suffered from the same illusions of grandeur, ignorance, or poor decision making as non-Jedi. The Jedi pre-Clone War were self-absorbed and so dependent on the Force telling them everything, they failed to actually observe their surroundings; other than Obi-Wan and Yoda, of course, who could tell something was up but just didn't understand the magnitude.
This same concept is found all through other Star Wars lore.