In 1687 Sir Isaac Newton published his Laws of Motion, the second of which states that "the mutual forces of action and reaction between two bodies are equal, opposite and collinear."
It's often occurred to me that basic laws such as this could be applied on a much wider basis to incorporate human interaction as well as the physical movement of inanimate objects. His second law, for example, must have lots of broader application in the World we live in today.
Haven't you seen lots of examples where the consequences of an action is diametrically opposite to that which was intended? Buying the wife a lovely Ab Trimming Machine for her birthday, for example? Or invading Iraq?
My most recent example is installing a high-tech, green energy, self-charging Mole deterrent in the garden. It seems to have attracted the little buggers.