The Principle of boomerang; What goes around shall come around.
The collective unconscious of our minds form an energy that connects all living forms in this world. This collective unconscious guides our fate, its a phenomenon that is a known fact. Some people call it karma.
To prove that this collective unconscious or this immense energy connects all living things and influences the cause and effect of one's life, scientists performed an experiment using rats. The rats were put in a complicated maze where they had to find a piece of hidden cheese while they were being timed. Then after it was done on some rats, they changed venue to another location and used the rats that lived there. The early rats in time had mastered the location of the cheese compared to their initial timings, however the new bunch of rats performed it just the same without any initial trial and error. Proving that the knowledge and instinct developed by the first experimented rats were passed on to their counterparts in a farther location through their collective unconscious.
Just like when a civilization in a far part of the world discovered the wheel, and without any contact with each other another civilization discovers it soon there after. The knowledge is shared by the collective unconscious of the human race.
The principle of boomerang says that what you do, or say or think will go into our collective unconscious and that energy will come back to us in a similar form. So if we send out negative vibes, then negative vibes will come to us like a boomerang. So if we do, say or think positive good thoughts, then good things will come to us.
Remember, what goes around shall come around. Spread good karma, brighten your aura.