On a fundamental level, we cannot be truly happy if we are not satisfied. When we are enamored with worldly existence, we are also subject to its nature which is unsatisfactory. No single material reward can suffice to quench our craving for such results. Therefore, when we pursue a preference for one worldly result over another we also confine ourselves to a mundane existence.
Making such a choice is not surprising if we have not experienced anything other than mundane happiness, i.e., if our only relationship to happiness is through temporary satisfaction of craving, how would we know that we can aim for anything different? The Buddha, however, pointed out that a different way to live does exist. We do not need to be confined to an endless cycle of craving.
What is the alternative? If we can see the benefits of positive, negative and neutral feelings, then we do not need to attach to any one of them. The benefits of positive feelings seem obvious but upon deeper reflection, one can see how boring life would be without challenge. And too much energy, whether positive or negative can eventually wear tired and so there is a benefit to relaxed neutrality as well.
If we pay careful attention to what is happening, we can see that all phenomena, as they arise and cease, are subject to suffering when we grasp onto them. But equally apparent from observation is the fact that we have the capacity to rise above the difficulty caused by the changing nature of reality. That capacity can be strengthened through the formal practice of mindfulness. Consequently, as we slowly integrate mindfulness into our everyday life, we also slowly adjust from being subordinate to changing tides of life to rising above them.