~Yoda Explains About the Force~
Yoda: A Jedi’s strength flows from the Force. But beware of the dark side. Anger, fear, aggression; the dark side of the Force are they. Easily they flow, quick to join you in a fight. If once you start down the dark path, forever will it dominate your destiny, consume you it will… 
Luke: Is the dark side stronger? 
Yoda: No, no, no. Quicker, easier, more seductive. 
Luke: But how am I to know the good side from the bad? 
Yoda: You will know… when you are calm, at peace, passive. A Jedi uses the Force for knowledge and defense, NEVER for attack.