Le Chatelier's principle is a useful expression of equilibrium in chemistry. It was probably the most important thing I learnt in A-level (high-school) chemistry. Briefly put it explains how equilibrium systems react to change - in effect any system tends to respond to oppose the change imposed on it.
I won't bore the non-science types any further (go read the link) but I was thinking that this basic idea can also be applied to human behaviour and is, in part, linked to the Law of Unintended Consequences. Something politicians, and others who would impose their views on others, could do well to think about.
Whenever we get new laws, decrees, taxes, doctrine, there is a reaction that tends to resist. Raise taxes and tax avoidance and evasion go up. Start cracking down on one crime and the criminals try something else. impose a new speed limit (or worse, a speed camera) and drivers find another route. Societal response is never as cut and dried as those who study it might have use believe. It leads me to have an instinctive skeptical response to anyone who tries to frame such issues in black-white, yes-no terms. It's not that easy and the choices are difficult.
In the end, I want more careful thought from those making the decisions. Weigh up the alternatives, the benefits, the consequences. And realise you'll never achieve the benefits you hope.