Why Do We Put Up With Unhappiness?

Most people, I think, would say they try to be happy. They want to construct their lives in such a way as to maximize happiness (however they might define ‘happiness’).

But in reality, unhappiness abounds. Unrest radiates from nearly every news broadcast. Stress levels deprive us of sleep, lead to overeating, and generally make us unhealthy.

Where does this discontinuity between desire (happiness) and reality (unhappiness) come from? If someone wants to be happy, why aren’t they? Why do we put up with unhappiness?

Related questions: Is happiness the most important purpose in life? What motivates us? Why don’t we know what makes us happy?