Variance
We give "luck" a fancy name..."VARIANCE."  It's quite simply the way that in reality, cards fall contrary to the predicted mathematical norm or average.  By the computed percentages, a player should win aprox 48% of the hands played and the dealer, the 52% left over.  Play it long enough, and those will hold true.  However, in the short term, that variance can really get lopsided....such happens when you loose 11 in a row!  No way to predict when it's going to happen.  If you could, it wouldn't be gambling.  Even those who count cards can't depend on it for a short session.  Even though a count is very high, it is no guarantee that the player is going to win....it's just more likely that he will.