Yoda: Yes, run. Yes. 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, as it did Obi-Wan's apprentice.
Luke: Vader. Is the dark side stronger?
Yoda: No, no. Quicker, easier, more seductive.
Luke: 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.
Luke: But tell me why I can't...
Yoda: No. There is no why. Nothing more will I teach you today.
Clear your mind of questions.
STAR WARS Episode V The Empire Strikes Back