In DesCartes' time reason was not opposed by emotion as it is for us, but rather to empiricism. We would say logic vs evidence. There was a tremendous debate on how the mind made up its thoughts, with logic or evidence (by which they meant what we receive through our senses). By beginning at thought DesCartes went on to find what he could know. He began with what seemed to him undoubtable. The only thing he could be sure of (that he thinks therefore must exist). So he took the side of reason over empiricism. For his time this was an important discussion. It is not for us as we know that the mind uses many sources to decide things. The kinds of things you work with Karen would be quite alien to DesCarte. It would take another few centuries to build psychology into a science and a practice. He and other Enlightenment philosophers were suspicious of emotions seeing them as desires and unpredictable. Remember, few people were educated so the idea of thinking through a problem was still in its infancy. Philosophy always needs to be put into context or we miss what is really being said.