Complex physical/mental attributes.

The human being is overwhelmed by the complexity of the physical body and overestimates his/her grasp of the complexity of the mental body. No one is as smart as they think they are.  

Dangerous experts

Financial and other "experts' are supposed to keep us out of trouble, not lead us into it. Are the "experts" who created the economic trouble really experts, or simply opportunists?

Experts fail when their "special knowledge" causes them to weaken valid statistical predictions because they "know more" or :"know essential facts."

But then, bad predictions are forgotten and often buried in reasonable-sounding explanations.