law of return
Also known as the "Threefold Law" or the "Rule of Three"
There are many variations of the phrasing of the Threefold Law, but it generally goes something like:
Ever Mind The Rule Of Three
Three Times Your Acts Return To Thee
This Lesson Well, Thou Must Learn
Thou Only Gets What Thee Dost Earn1
When you take a resource, even with good intentions, there will be repercussions. The petty cash box will soon be empty if one doesn't occasionally put money into it as well as take it out. Actions need to be balanced, or else things can get quite out of control to a degree many times over that of the original issue.
In other words, there's no such thing as a free lunch.
Other phrasings emphasize completely separate issues, which author Phyllis Curott has recently taken to calling the Boomerang Whammy Rule:2
Mind the Threefold Law you should,
Three times bad and three times good.
The above version was taken directly from the Rede of the Wiccae, a piece of work that I do not believe is required reading for Wiccans but is interesting to investigate at the least. Or, for an even more extreme version:
Ensure that your actions are honorable,
for all that you do shall return to you, threefold, good or bane.