An epic battle has raged on since the start of human existence; the battle between certainty and rationality. And it’s fought within our culture, our businesses, and even within our very minds. Rationality is deriving from evidence what is correct. Despite being very different, both perspectives find their way into the same conversations, the same strategic approaches, and the same Big Data and data science methodologies. When not handled right, these perspectives impede the success of Big Data and the models that support it. Let’s explore the differences between certainty and rationality, understand why they historically exist, and increase our awareness for which perspective we’re speaking from.