“One of my favorite Paul Krugman papers is called “Ricardo’s difficult idea” — on why people have such a hard time understanding the concept of “comparative advantage.” Although the situation is not quite as bad, I’ve been struck recently by how much difficulty many people have trying to understand the concept of a “collective action problem.” Although that idea has a bit more history to it, I don’t think it’s too much of a distortion of the record to call this “Hobbes’s difficult idea.””