In some of the stuff I have read, jedi go dark because of war, hate, love, envy, some kid snubbed you in class, etc. Basically any strong emotion makes a jedi "Dark" according to the books/games/stories, which I think is bunk. You can be passionate about something without doing evil stuff. I am still looking forward to the next star wars film. I just wanna see the jedi wiped off the galaxy!