CronoDAS may already have said this, but just to elaborate a bit: one might wonder if sadness increases useful theory revision, and thereby increases aspects of rationality. And one might conversely wonder if the modes of thinking that prompt useful theory-revision, rather than speeches for coherent social posturing, tend to directly increase sadness. (Not because they cause us to notice sad things, but because hanging out in those modes of thought is itself a sadness-associated activity, like frowning.)

By way of analogy: happiness causes smiling, actively working on projects, and perhaps socializing, and forcing yourself to smile, to start projects, or to socialize probably increases happiness. (I've seen studies backing up the active work effect also, but I can't find them.)