I'd dearly like to think that this is true, but at the same time reciprocation isn't a good reason  for one's actions.  Do the right thing, regardless of benefit or consequence.

I believe this is very true.  It just seems to work out that way.

This is  basic law of nature and you can count on it.

I could make a lewd joke about this... but I won't

Or "you reap what you sow". There are many different ways of expressing this dictum, but no matter what, the idea is the same: outcomes in life are determined by the kind of effort you put into any given task. If you do things correctly, you'll get a good result, if you don't, the negative happens.

I don't say it much as I did when I was a kid but it'll always happen no matter what.

Karma is all around you! You get what you give, so think next time.

I live by this credo.

Yes, Molfan, one of the best phrases used to express a desire for justice.

I like this one and hope it comes true especially if i am referring to someone who is a creep. I would love to see someone who is nasty to others get a bit of their own come back to them. or on the other hand if someone who has always been terrific get something great happen to them. can go either way.