Also known as the Three Fold Law, is a rule held by Wiccans/Pagans and some Occultists.
It is believed that whatever energy you put out into the universe, be it positive or negative, that it will come back to you three fold.
However, it is a rule that is not followed by every Wiccan or Pagan and is highly contested in modern time with many asking is The Rule of Three real or just a made up rule to keep followers on the 'right path'
Whatever you believe, if it keeps those practising rituals and spell work, from casting harmful spells or at least taking some serious consideration into doing so then, true or false, its an ok rule in our book! After all, if you surround yourself with good things and send positive energy out into the universe then good things should come back to you right?. Living your life with negativity in it will often bring more negativity into your life. Whether that's karmic forces of The Law of Three or just the universes Law of Attraction that's for you to decide.
And Why the Law of Three and not The Law of 4 or 10?
Three is well known as a magickal number. However, it doesn't mean that if you punch someone in the face at work then you're payback will be; being punched back in the face three times! What it could mean though, is that you lose your job and your employer refuses to give a positive reference to future employers. Which in itself could be deemed as 3 times worse than being punched on the face.
So, do we follow the Law of Three? Well No, but we do believe that energy is reciprocal and so what you put out there comes back to you.
Ultimately, it is up to you to manage your own behaviour, both in every day life and in magick. Accept responsibility for your actions and always think before you act.