Opportunity Costs

...There are really only two things that you have to know about economics. As with, say, the two things about boxing: hit, don't get hit. In economics these are 1) incentives matter and 2) opportunity costs. The first of these we all intuitively grasp, the second sadly vast swathes of the country do not. And the wish is that we get the education system sufficiently sorted out so that every child does indeed understand this vital idea.x

Tim Worstall, http://www.adamsmith.org/blog