You only get by what you give. So, I like to believe it's true!

I like to think that we are all like some kind of "channel" for wealth and other stuff that have nothing to do with your question.

Maybe it's because when we give we are less attached to the stuff we're giving away. No matter what we are giving, it will come back to us. The universe doesn't like to have debts towards us.

It's like when we are in Love. If you get so attached or dependent of a person and you try to keep her/him for yourself, most likely you end up losing the person. But when you give it trust and let them fly away they will eventually come back to you.