I suspect that you cannot recall any truly significant action in your life that wasnt governed by two very simple rules: staying away from something that would feed bad, or trying to accomplish something that would feel good. This law of approach and avoidance dictates most of human and animal behavior from a very early age. The forces that implement this law are positive and negative emotions. Emotions make us do things, as the name suggests (remove the first letter from the word). They motivate our remarkable achievements, incite us to try again when we fail, keep us safe from potential harm, urge us to accomplish rewarding and beneficial outcomes, and compel us to cultivate social and romantic relationships. In short, emotions in appropriate amounts make life worth living. They offer a healthy and vital existence, psychologically and biologically speaking. Take them away, and you face a sterile existence with no highs or lows to speak of. Emotionless, you will simply exist, rather than live.

Why We Sleep by Matthew Walker