I never thought Star Wars would be so deep. I mean, it’s only a science fiction with a lot of fights and funky machines, right? Apparently not.
(Spoiler alert!) Anakin (good guy) finds out that his wife is going to die in childbirth. Lord Sidious (evil guy) lures Anakin to join his side (the dark side) by promising to teach him powers to stop people from dying. Anakin changes sides, and before even he could start learning the powers, his wife dies. Anakin continues to stay with Lord Sidious, however.
Now, if Anakin really only wanted to save his wife and if he didn’t really have the ‘power lust’, he should have left the dark side and gone back to where he belongs—to the Jedis. But he decides to stay on the dark side. Maybe saving his wife was just an excuse he had for himself... he was fooling himself thinking that he’s doing it out of love while in fact he was only after power. It can be argued that he didn’t go back because the Jedis wouldn’t accept him again after all he had done. That again goes back to the fear of losing his position.
Master Yoda would say in a scene, “The fear of loss is a path to the dark side”. Anakin proves that by transforming into Darth Vader.