The Motley Fool seems to have forgotten this, but rational-agent theory is a useful fiction, not a statement of reality. The best analogy I can think of is Skinner's behaviorism; rational-agent theory seems to fail in the same kinds of places as behaviorism does, too.<p>Look up the "Ultimatum Game" for a particularly effective demonstration of where it fails -- and the commenter here who points out that rational-agent theory would destroy civilizations is completely correct. (Mental exercise: apply "the tragedy of the commons" to a defensive war.)