Yoda:
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, no. Quicker, easier, more seductive.

Luke:
But how am I to know the good side from the bad?

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Yoda:
You will know… when you are calm, at peace, passive. A Jedi uses the Force for knowledge and defense, never for attack.