Certain paradigms, theorists, and problems are in, and some are out, and not being both aware of this and following it can be a fast track to professional irrelevance. Science and philosophy are particularly brutal in this respect, disciplines that even at their most charitable are sometimes apt to narrate their own histories — even very recent histories — as stories of venerable idiots doing the best with what they had. I have spoken to mathematicians, biologists, psychiatrists, and economists, and — when they are sure nobody else is listening — they confess that this is often the case in their disciplines: The movements of their field are like the movements of a mob, perhaps just as unpredictable over the long term and equally difficult to resist.