Yoda was a miserable little green failure in almost every way imaginable. All of his powers did not allow him to see what was plain before him, and apparently at 900 years, he had ample time to undercover the machinations of the Sith. He could have listened to others like Qui Gon but he waited until it was too late, and this lack of leadership must have certainly spread like a cancer among the other moribund masters. It is easy to see a living force rejecting that dead wood in favor or some new form of balance, the harbinger of a new order.
Rather than take Anakin under his tutelage, realizing the danger of either letting him go or letting an inexperienced new knight like Obi Wan train him, he opted for the latter. He got embroiled in republic politics, despite whatever moral code he espoused, perfectly willing to use sentient clones like cannon fodder (how is he any different from Palpy, in that regard?) His continual blunders may have helped cost billions, even trillions of lives. That he failed in his last ditch fight with Palpatine is just a cherry on the top of a sundae of loss. Of course by then he could only instill upon Luke a certain amount of training, leaving him ill prepared to teach students of his own, which is obvious by the fact that Luke nearly murdered one of them.
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