The "butterfly effect" is only possible in some classic systems. For example imagine that you put a drop of ink in a glass of water (with some sugar). If a butterfly drinks some water, it will not change the final equilibrium state where the ink is evenly distributed.<p>This prove that one particular quantum system does not have an important butterfly effect, not that any quantum system does not have a butterfly effect.<p>(Note that r(as far as we know) reality is described by quantum mechanics. So it they prove that any quantum system does not have a butterfly effect, then the weather and all the other macroscopic systems do not have a butterfly effect.)