The desire to attain happiness is the sole cause of unhappiness. We think by changing something in the physical world that we will attain a state of happiness. Trouble is the nature of the collective, physical world is always being influenced and thus changing. So by being attached to an outcome in the physical changing world to get our state of happiness, we are literally chasing a moving target that will never be reached and or maintained. So chasing happiness is ultimately a fruitless venture. You have heard of people trying to find themselves by moving around the physical world and exploring it. The real journey of self discover is within our own being.
By chasing happiness we set up a conflict loop. We don't accept our current state and feel a need to change it. We don't understand it is a decision away at any time in how we interpret things. We project reality. But when we take our cues from the stage (physical world) we are trying make edits to our reality at the level of second cause. Impossible. The place to make changes is at the primary spiritual level of reality. And for now most of us can do this through our emotions which are more powerful that mental thought forms in creating change. Together, harmonized they become powerful allies.