Happiness is just a neurochemical spurt. Four different brain chemicals create happy feelings, and you need all of them to feel good. You miss out when you rely on one or two old familiar ways of triggering your happy chemicals. You can enjoy a balanced happy chemical diet if you know the distinct kind of happiness each brain chemical evolved for.
Endorphin happiness is triggered by physical pain. The body's natural morphine masks pain, which allowed our ancestors to run from predators when injured. Humans experience endorphin as euphoria, but it obviously did not evolve to trigger a constant feeling of joy. You would touch hot stoves and run on a broken leg if your brain were always releasing endorphins. Nature saves them for moments when they help you do what's necessary to survive.
Dopamine happiness is triggered when you get a new reward. When you see a finish line, your brain releases dopamine. It's nature's reserve tank of energy. Dopamine keeps you going until you catch the prey you've been stalking, even when the chase is long and frustrating. If you surged with dopamine all the time, your energy would be depleted when you really needed it. We evolved to save dopamine for those moments when an important goal is within reach.
Oxytocin happiness is triggered when we trust those around us. It promotes bonding between mother and child, and between sex partners. It's stimulated when you're with a group of like-minded people, or when you get a massage. But we did not evolved to feel oxytocin happiness all the time because there's no survival value in trusting people who are not trustworthy.
Serotonin happiness is triggered when you feel important. Animals release serotonin when they dominate a resource. Their serotonin falls when they cede a resource to avoid conflict. Being one-up feels good, but conflict can cause painful injuries. The brain is constantly analyzing information to balance the risk of pain against the satisfaction of winning.
Each of the happy chemicals evolved to do a job. They work by making you feel good, which motivates you to go after whatever triggered them. You have inherited a brain that motivates you to go toward anything that promotes the survival of your DNA.
Sometimes you stumble on happiness. When an ape accidentally stumbles on a luscious fruit tree, its brain surges with dopamine. That creates memory, which helps the ape find the tree in the future. New rewards trigger dopamine whether the rewards came by accident or with sustained effort.
The happy chemicals feel so good that we use our big cortex to figure out how to get more. Apes negotiate groomings with each other, and it stimulates their oxytocin. Apes dominate their troop-mates when they think they can get away with it, which stimulates their serotonin. Apes invest time teasing termites out of a mound, and it stimulates their dopamine. Apes are not known to hurt themselves in order to get an endorphin high. People do all kinds of things once they find that it stimulates their endorphins, or their dopamine, or their oxytocin, or their serotonin.
Sometimes it works.
But the brain only releases happy chemicals in limited bursts for specific aims. It did not evolve to release them all the time. If happy chemicals flowed all the time, they could not do their jobs.
When your happy chemicals dip, however, you notice. Something feels wrong.
Nothing is wrong. Your happy chemicals evolved to ebb and flow. But if you attend to this feeling that something is wrong, it can preoccupy you. Your cortex will scan the environment for evidence that something is, in fact, wrong. And it will find evidence to confirm that feeling.
If you expect all the happy chemicals all the time, you're going to be disappointed. And if you focus on that disappointment, you wire your brain to see the world through that lens.
Try as you might, you can't control your environment in a way that ensures a steady flow of happy chemicals.
You could instead accept the fact that happy chemicals evolved to promote survival behaviors, and just appreciate them as they come and go.
My book Habits of a Happy Brain: Retrain Your Brain to Boost Your Serotonin, Dopamine, Oxytocin, & Endorphin Levels shows how anyone can build new neural pathways to their happy chemicals. When you feed your brain with new happy-chemical strategies, it frees you to stop using and abusing the ones you are already relying on. Free downloads on your happy chemicals at Inner Mammal Institute.org (just below the books), and on my Psychology Today bio page under "Research Papers."