The law of three is the idea that our actions return to us, either multiply, threefold, or until we "get it". But is this a magic only idea? Or is it a universal ethic...
I believe that our actions return to us regardless of whether they are "magical" or not. If the don't return to us in this life, then they will the next. I DONT believe that all bad things happen because of this though. I truly believe that there is Chaos in the universe, and luck and that we are presented with challenges and lessons irregardless of how "good or bad" we are.
I personally see the "law of three" this way:
First there is Atonement or Reward. You receive appropriate "payback" for what you have done good or bad. The punishment USUALLY fits the crime in some way, often ironically in my experience.
Second there is Learning, you must either learn what you did - right or wrong and the lesson of that experience. Until you learn you are doomed to either be punished again for your actions - or lose or squander your reward.
Third there is Growth. You must reapply the knowledge you learned to your life and grow from it. People who learn but do not grow are haunted by their mistakes and failures . Once you have grown you are free of the cycle of repeating the past steps... for that action.
So you see your actions return "times three" - but some people have more or less "consequences" depending on their ability to move forward through the process of change. Since many of our actions can be seen on a broad scope, if you do something in your heart you feel is best- and it results in "bad," you will not be punished as if you did something pointedly treacherous.
The law of three is a principle... a natural occurrence. In a way it is very handy- because you can measure how much "bad" will return to you for any action, approximately, and also how much "good" as well.
That stated... we SHOULD be ethical, trustworthy descent people, not for fear of consequences or promise of reward, but for personal integrity alone.