Well, I see humans sometimes as simple machines. We have
  anticipation/expectation mechanisms always functioning. We have
  receptors that bring in reality. Then we have comparators
  inbetween. [yes, it's a computational metaphor] When the
  anticipation doesn't match up to reality, we react. In short,
  these reactions are expansions of cognitive dissonance. Of
  course, computational metaphors aren't as fun as evolutionary
  ones smile emoticon