Happiness is a surge of dopamine, serotonin, oxytocin or endorphin. These brain chemicals turn on and off for reasons that are hard to make sense of until you know how they work in other animals. Then it's easy to see how our happy chemicals are stimulated by behaviors that promote survival in the state of nature. Unhappy chemicals (cortisol) surge when you see survival threats. Your brain defines survival with circuits you built in youth. You can build new circuits, but it's harder than you expect. It's not easy being a mammal, but it helps to know how your operating system works.