6. Emotions are chemical reactions that arise in nature to guide and aid actions - this is the survival instinct. Reason arises in nature to help life choose between actions that satisfy short-term desires or long-term needs. We are not bound by any laws of nature to act on every emotional state we feel. The joy of the survival of life is our deepest feeling so reason can be said to serve that emotion, but reason rules over other emotions as it instructs us about which actions we should take and which emotions we should feel.
I'll delve further into the causes of emotion a little later, but for now I just want to place a little more emphasis on why reason guides emotion. For many decisions that we face, the answer can be pretty obvious: should I run from this snake?, should I avoid touching this hot stove?, should I hold onto this railing while I walk past this ledge? Our emotions are clear and unambiguous in these situations (either from innate inheritance, early trial and error, or overwhelming social influence), and we can happily listen to them and quickly make the right decision. That's fine. But these are not the only types of decisions we face. Most of the time, our emotions are ambiguous or conflicting over our innocuous or important decisions: should I go out or stay in?, should I eat that piece of cake?, who should I vote for?, what should I study in school?, should I marry this person? It is these types of complex decisions where we cannot simply "listen to our hearts," but must use reason to decide what is best for us. When we don't do this, we are living the unexamined life. When we do this well, our hearts will follow, and we will be happy.