I think of this question in terms of Emergence which was defined by G.H. Mead in The Philosophy of the Present, as a discontinuity in our understanding of things in which a new way of seeing things or a new thing comes into existence, and reorganizes everything that was there before so that we see history in a new light, we see possibilities that we never noticed before and we have new affordances or options for doing things in the present. So for instance smart phones are going to allow us to interact and do things in ways we never could before. There are different scopes at which an emergent event can occur, which are Givens, Facts, Theories, Paradigms, Epistemes, Ontos, Existences, Absolutes. When an emergent event occurs then it perhaps slowly but necessarily rearranges our experience of everything else in the world within its scope.
So a really original thought is one that sets off a cascade of emergence that rearranges the way we see the world. But a non-genuine emergence increases the background nihilism that makes it possible for us to see an emergent event when it occurs. So original thoughts are probably rare in this sense of something that sets off a genuine emergence. But they do occur. And in fact they fracture our tradition with discontinuities when they occur as Black Swan events (Taleb).