In his book Thinking Fast and Slow, psychologist Daniel Kahneman describes two ways that humans process information. There is a fast process that is intuitive and instinctive, and there is a slow process that is more deliberate and careful. He calls the former System One and the latter System Two. We may use System Two to make a more thoughtful decision. However, Kahneman emphasizes that often we engage System Two not to make a decision but instead to rationalize a conclusion reached by System One.

