By and large, humans are not good at thinking rationally, but, really, who can blame us? We have not had much practice at it. According to the accepted wisdom of anthropologists and paleontologists, by no later than 12,000 B.C.E. – approximately 14 millennia ago – humans already had spread to and settled in every continent on the planet except Antarctica. Yet we only started to make rational sense of our existence a few hundred years ago. Prior to the mid-seventeenth century, nearly all human understanding of ourselves and our world arose out of a mythic, poetic, narrative sense – not a rational one. Of course, that is because “rationality” – properly understood – is not a concept easily embraced by humans. We are drawn to certainty and to firm, fixed answers, but for an idea to be rational it must be capable of being proved false. To embrace rationality means to embrace uncertainty, rationality’s essence.