The reason this is the case is that in most cases, simply knowing the direction of some news event is not enough to predict the reaction in a stock. If only it

The reason this is the case is that in most cases, simply knowing the direction of some news event is not enough to predict the reaction in a stock. If only it was so simple, linear and one dimensional. Generally the reaction of a stock has about a dozen inputs ranging from other market participants expectations, macro/rates, broader market, politics, etc. On other participants expectations alone.. You might see a news story like "Apple ships record number of iPads" and go wow great, I should have bought Apple yesterday. But you don't know what other participants expected in terms of number of iPads shipped. Further, you don't know what metric of Apples earnings report that other participants were tracking most closely. What if it was gross margin on iPads sold, and while the units sold went up.. it was all in a newer lower end priced model that dragged down overall margin in the segment? Further what other news did you miss - what if in some parallel dimension of this game, there was a news story on page 5 about MSFT/GOOG shipping a truly competent iPad competitor. Or what if what other investors respond to is some aside comment made on the earnings call regarding an expected slowdown in services revenue?