I'll repost an old post of mine for this, as I think it's extremely applicable. Had Qui-Gon trained Anakin, I fully believe that Anakin would have fulfilled his destiny as the Chosen One without ever falling to the dark side:
==========================
Interesting theory, but I don't think he was a Sith. Rather, I think he may have been much as Dooku said he was. Had he lived, I could definitely see him joining the separatists. And this is what I don't like about Lucas' concept of the force, really.
From all appearances, Lucas got his idea of the Force from Taoism. The way he's represented it, the Yin is "light" and the Yang is "dark". That's not how it should have happened. Striving for enlightenment, harmony, and peace should have been light, and striving to manipulate and conquer should have been dark. That said, to be enlightened, and live in harmony and peace, it is not required that someone abide by the rules that the Jedi order set down. It is possible- someone like, say, Walt Whitman would say *only* possible- to attain the balance and harmony through understanding and living within your own emotions.
Thats where I think Qui Gon was, in spite of the Jedi Order telling him it was wrong, and it's the state of mind that I think Anakin tried to find. The reason that he fell to the Dark Side was because he felt such intense emotion, yet he was taught on one hand (Palpatine) to embrace it and use it as a force to strike down the Order, and on the other hand (the Council) he was taught to ignore it entirely. Anakin wanted to be good, and would have been good, if not for the gross negligence of the Jedi Order. My theory, therefore, is that had Qui-Gon lived to tutor Anakin, he would never have fallen to the Dark Side. Qui-Gon would have taught Anakin the truths that the Order, for some reason, denied- that fear and love can be embraced for the ultimate good. Anakin's fall is as much at the hands of the Order as it is at the hands of Palpatine. The only difference is that one does it unwittingly.
And this, in my opinion, is why Darth Maul seems so intent on killing Qui-Gon specifically in Episode I. I bet Sidious knows that if he can eliminate the only 'romantic' (in the philosophical sense) in the Jedi Order, Anakin will have nobody left to turn to with his emotions but him. Qui Gon is, basically, Anakin had Anakin found a way to reconcile his emotions with the Order's teachings.