The Chosen One Arrives
This brings us to episode I. Qui-Gonn finds Anakin fascinating, but it is not until Shmi says there was no father that Qui-Gonn’s mind goes crazy. He trusts the prophecies and believes Anakin is the Chosen One. It has been theorized by some that Darth Sidious’ greatest enemy was actually Qui-Gonn. Had he lived past the duel with Maul, his attunement to the prophesies and the living force may have unraveled all Sidious set in motion.
While it hurt Obi-wan’s pride, Qui-Gonn’s devotion to Anakin above all else was driven by the prophecies. Qui-Gonn knew Anakin was the key to the future. This is why his dying breath was towards Anakin, not Obi-Wan.
Fall of the Jedi/Rise of the Dark Side
During Revenge of the Sith, all of the prophesies were in motion, but nothing had changed yet. It was not until Order 66 that the balance shifted. a thousand years of light would soon fall to darkness.
With Order 66 issued, hundreds of Jedi died at the hands of clones. More would die when Lord Vader attacks the temple. In a very short time the Jedi are all but extinguished. One huge thing to keep in mind is that not all Jedi were killed during this purge. A small handful of Jedi would survive, scattered throughout the galaxy. Some would be hunted down by Vader and his assassins, but even then some remain – force users, but no longer Jedi.
The balance has now switched. A thousand years of light have been replaced by the dark side. Only two may exist, but those two control the galaxy, and there are no light side users to oppose them. The force spins out of balance in the other direction.