Its all qui-gons fault!!!
If you trace the chain of events back far enough, the fall of the jedi is all qui-gons fault. DAMN him for having rogue ideas!!!
Qui-gon beleives in the living force. the jedi council doesnt. he is defiant, does not follow some part of the code, probably in his beleif in the living force is part of it. he trains obiwan. yoda senses qui-gons same defiant attitude in obi-wan. obi-wan arrogantly assumes to take anakin as his padawan learner, even if he must without the councils approval. although he does get the councils approval, he still has qui-gons defiance. that no doubt affects how he trains anakin. anakin doesnt learn the control necessary to remain a jedi, so he turns into a sith and plays a pivotal role in wiping out the jedi.
"i thought i could train him just as well as yoda. i was wrong."