It’s not about accuracy. If a stock is priced at a huge multiple to earnings and sales, the market consensus is enormous profit growth for a sustained period. When the slope of the curve moves (or changes direction) the NPV (Net Present Value) of future cash flows drops dramatically.
The miss is also against future guidance. This could be answering a question of “Is Facebook too distracted to grow their core business?”
Anyone who thinks they’re more rational than the market can take the other side of these large moves. (Many quant hedge funds do)