On Quora, I was asked where economics works. I changed the question to “which concepts work?” My answer was
The laws of supply and demand work. The principle of substitution works (we do not run out of resources—we substitute away from resources as they become scarce). The idea that economic growth involves creative destruction works. The idea that specialization and trade are fundamental elements of economic behavior works.
Concepts that do not work, in my opinion: aggregate demand and aggregate supply; neoclassical model of income distribution; theory of public goods–it is clearly wrong as a positive theory of how government behaves, and because it is wrong as a positive theory its normative value is also quite dubious.
I would be curious about how other economics bloggers might answer this question.