I have heard a couple of times "Keynesian economics discredited" (or just the term "discredited") thrown around, but where does this line of thought come from?

I have heard a couple of times "Keynesian economics discredited" (or just the term "discredited") thrown around, but where does this line of thought come from? My (lay) impression was that Keynesianism had resurged over the past couple of decades due to the failure of more free market and/or austerity economics, especially in Europe.