Humans have emotions as Millman has already observed.  And it is clear removing emotions from the "cognitive equation" affects the ability of humans to cognate - see Damasio Descarte's Error, & etc.  Predisposition to over weigh, relative to objective valuation, one's education and the results of that education plus past experience and data plus emotional commitment to such leads to 'thinking dysfunction' as as the link shows with additional evidence from Taleb in his book Black Swan.  Now toss in Altemeyer's work on Right Wing Authoritarians and his analysis of their basic episto-psychology.

And it we begin to get a glimpse that human decision making isn't "irrational," per se, but, rather, a complex melange of rationality (Critical Thinking) as embedded in the mesolimbic and mesocortical pathways, among others.  

Aristotle got it wrong.  Humans aren't "the rational animal." We are animals capable, subject to a galumphing horde of limitations, of choosing to be rational.

Ever since I learnt about confirmation bias I've started seeing it everywhere