The Law of Return

'Early agriculturalists accepted "the law of return", which simply meant that the farmer should try and repay the earth for what he took from it. But he did not sit at his fireside and chew his nails, asking himself whether he got the best of the bargain. It was not a "law" which worried him - it was just clearly the right thing to do.

Cradle to Cradle is a law of return but with materials rather than food-crops.'

From: Cradle to Cradle: Remaking the Way we Make Things.