Happiness is transient. Physiologically, happiness is a temporary boost in the neurotransmitter dopamine. This dopamine boost gives you the feeling we call happiness.
But that boost is impossible to sustain beyond a few hours. Your brain eventually shuts down the production of dopamine and you revert back to your dopamine, or happiness, baseline. So, if happiness is your goal, it is one you will always fail to achieve.
Instead, fulfillment should be your goal. Fulfillment is the feeling associated with doing something that is meaningful and rewarding. When you are engaged in activities that you are passionate about, that triggers the emotional part of the brain, every time you engage in the activity. When your emotional brain is engaged in activities that you are passionate about, it gives you a feeling of fulfillment that lasts for as long as you are engaged in that activity. This could be months, years or a lifetime.
Fulfillment should be your goal, not happiness. Find your passion, engage in it every day, and you will find fulfillment.