That saying assumes a rational market, and while there is some evidence that the average human behavior trends towards the rational there are plenty of evidence against individual behavior being rational (see homo economicus).

As more and more wealth get distrubuted to fewer and fewer hands, and as fewer and fewer extremely rich individuals control more and more of the market, My gut feeling is that if the market was ever rational (which btw. I am not entirely convinced of) that very much no longer holds true.