Most of our decision making comes from own emotions. As a cognitively evolving species, we continue to choose based on how we feel about someone or something and ignoring reason. Those feelings, most of the time, outweigh reason. Without reason or understanding why we are feeling a certain way always leads to poor decision making, thus, becoming unhappy.
The happiest people are those who can blend their own reason abilities and emotions simultaneously. It is a learned skill not innate, so there is hope for everyone. Anyone can witness such greatness by just watching a mother be fully engaged with her infant.