Emotion is energy, and in order to cause change, it must move.
Where does it move first? Through you.
Hate, like fear and anger and love and sorrow, is an emotion, and emotion is energy, so in order to be expressed, it must first move through you. So when you feel hatred toward another person, you're casting hate upon yourself first.
The same is true of love, and peace, and joy.
It's not a matter of "what you send out you get back times three." What you send out doesn't just come back to you--it starts with you.
Any emotion you try to horde will turn stagnant and fester inside you--to help it grow, to help it heal, to share it with others, you have to let it flow.
We can make the conscious choice to direct our energies. We can raise the ones we want to encourage and ground the ones we want to be free of. We can work to transform energy from negative into positive and channel it into a kinder world, and in doing so transform ourselves...or we can hex ourselves with every heartbeat.
This is magic.