1. The idea that if you have a strong magickal defense, the result of a spell worked against you will bounce the negative current back to the sender like a boomerang returning to the person who threw it. Those who accept the three-fold law believe that the effect will be three times as potent as the attacking force.
2.Negative telepathic messages and psychic-energy transfers have a traditional "return to the sender" phenomenon noted in magical literature as bouncing back with a three-fold increase in power.