IF YOU DID NOT SEE THE STAR WARS MOVIES THERE IS A SPOILER AHEAD
In Star Wars Episode I - The Phantom Menace, Qui-Gon Jinn says Anakin will bring balance to the force, which he does. In Star Wars Episode VI - Return Of The Jedi Darth Vader kills Emperor Palpatine. Which is bringing balance to the force because Palpatine was the ruler of the Galactic Empire and he was bad. So Anakin did bring balance to the force, it just took him becoming Darth Vader, to do it.