“one view sees the constraints of the world as being the first thing you have to ask about, which is to say, when you look at a policy you don’t ask what are the goals of this policy, you ask: What incentive does this policy create? What constraints does it introduce and what are the likely consequences of those incentives and that constraint? You also then tend to think in terms of trade-offs rather than of solutions. So you don’t say we must get rid of greenhouse gases, you ask: What does it cost to get rid of greenhouse gases? How much will it cost if we don’t get rid of them? How much does it cost at each level of greenhouse gases and what are the consequences of not reducing it and so forth?

The other view really is more of a crusading view, that is, it’s an unconstrained vision. This is something that ought to be done, and therefore we pursue it as if it were the Holy Grail and we don’t have time to stop and muddle over a cost-benefit analysis”. –Thomas Sowell, explaining two different ways people look at policy, with economists using the first.