Have you ever done something or reacted a certain way, and then said, "Why the fuck did I do that?". I'll tell you why - because your brain was designed 70,000 years ago to reward you for actions that increased your chances for survival or reproduction. It goes something like this. Every time you do something your brain asks itself, "Did what this fool just do increase our chances for survival or making children?". If the answer is yes, your brain releases some dopamine (the feel-good drug) as a reward.
This is why we pursue food, sex, and social status as if they were drugs. But the world has changed on us. We're chasing a dopamine high for things that don't necessarily improve our chances of survival. Back when getting enough food was a challenge it was beneficial to be chemically rewarded for eating, but now that it is overly abundant this mechanism leads to over-eating and chronic disease.
In tribal days, social status was important for finding a mate, but now even after finding a mate we're still stuck in the endless loop of trying to impress others on Instabrag and Facebook. The caveman in us is still running the race for survival when in reality we've already crossed the finish line.
Our brain was designed for our survival... not for our happiness. However, we were given a tool - consciousness. We can be aware of our nature and therefore seek to master these things that no longer serve us. Be master of your dopamine.