Efficient at what?

The primary problem is people misinterpreting and overinterpreting EMH, often as not its proponents as its opponents. It actually says very little. Like Yglesias, if it were called the unpredictable market hypothesis, it would likely both be more widely accepted and less controversial. The problem is efficiency is equated to rationality but if markets were rational prices would not be subject to tectonic changes, nor would they vary widely from fundamentals. Markets may be efficient at reflecting our beliefs but our beliefs are not necessarily rational. Often people interpret it as markets may not be efficient but they tend towards efficiency (rationality). Yes, markets can stay and increase their irrationality longer than you can stay solvent, and when everyone is being irrational, there is efficiency in being irrational.

If one interprets information in an objective sense, then efficiency would imply rationality, but if one interprets it as future expectations, and especially as expectations of others expectations, then there can be no objectivity nor rationality because we are not considering the past but the future, all information concerns the past, and we are free to imagine any possible future. As future becomes past these expectations can swing wildly and imaginations can trample the hardiest of fundamentals. Imaginations are free to soar and plummet even as fundamentals keep us tethered to the realities of the past. Markets are efficient at reflecting our hopes and skepticism, greed and fear, dreams and nightmares.