Markets are tumbling. It's because the Fed is about to push up interest rates. Or maybe because the German economy is weak. Or perhaps it's Ebola, about to decimate global populations. Or it's geopolitical conflict - Ukraine, Syria, Iraq ... take your pick. It's a perfect storm. Head for the hills and don't spare the horses. And remember the shotgun.
Of course, it's none of these. Markets are falling because they were a bit overpriced and investors were ignoring the fact because they'd got themselves into a typical feeding frenzy, ignoring the risk and ambiguity that are always present. Now that they have recognized the issue they're fighting each other to get out the door. Which is why all of the explanations for market weakness are entirely plausible and entirely wrong - they're an example of what Nassim Taleb calls "the narrative fallacy".