Cause and Effect, and Magic

I have a bit of a problem with many people's ideas about "Cause and Effect" and the role it plays within magical practices. I know many people like to repeat at nauseum things found in books without much thought (this doesn't mean everyone, so don't get your panties in a bunch), but many people like to repeat an idea within physics that I don't think they really understand.

This whole idea about "cause and effect" returning energy to the sender or a loose form of the "Law of Three" I still don't understand how people can still cling to this idea like a security blanket.

In physics we understand the theory of motion..."for every action, there is an equal and opposite reaction". What is it then that the energy sent out is hitting to cause it's return to the sender? Energy (that which is sent out by a person) is in a sense particles, let's say. Everything is made up of energetic particles. In a sense, the way I see it, energy would either merge or go through objects or things in it's way...so what is this energy bouncing off of, to cause it's return to the sender?

Again, why I don't subscribe to this idea of "Law of Three" or "Law of Return". It doesn't make sense, metaphorically, or physically. For the "Threefold Law" to make sense or even work, it would have to violate this "Law of Motion", because of the simple fact that it states "for every action, there is an equal and opposite reaction". For the Threefold Law to work, the law of motion would say "for every action, there is a multiplied and opposite reaction". The Law of Motion doesn't work this way, therefore the "Threefold Law" doesn't make sense.