Here we discuss the inherent differences between classical and quantum physics. Systems representing both can exhibit "unpredictable" behaviour - so what is the difference? In classical physics chaos theory is a genuine phenomena - but only in theory. The real world does not obey classical physics. It obeys quantum theory and there, that kind of "chaos" simply does not happen. The Butterfly effect is therefore false in reality for reasons explained herein. Those classical effects cause classical systems to be unpredictable due to the sensitivity of systems to initial conditions which cannot be specified, or known, with perfect precision. But quantum systems can be "intractable" making them unpredictable for different reasons. Rather than being a barrier to knowledge and computation this is an opportunity. We discuss Feynman and then Deutsch's own contribution to the field of quantum computation.