:The Three-Fold Law:

The Three-Fold Law, or Law of Return is the belief and principle on which magic is used.

This law relates to the use of power and energy. When used, power is returned to the sender at three times the level it was sent out.

The most commonly used comparison is that of "The Golden Rule". Do unto others as you would have others do unto you.
You put out nastiness and nastiness will surely return to you.