This quote is in several articles online about happiness.
“First, your brain adjusts feelings of happiness downward after you’ve reached some goal or other. It regulates the good feelings, presumably so that you have motivation to reach the next goal instead of just lounging by the pool for the rest of your days. “
Which can sort of be related to the Matrix quote
Agent Smith: “Did you know that the first Matrix was designed to be a perfect human world? Where none suffered, where everyone would be happy. It was a disaster. No one would accept the program. Entire crops were lost. Some believed we lacked the programming language to describe your perfect world. But I believe that, as a species, human beings define their reality through suffering and misery. The perfect world was a dream that your primitive cerebrum kept trying to wake up from. Which is why the Matrix was redesigned to this: the peak of your civilization.”
Interesting what biochemical reactions can do to us and our lives.  Seems to be that way for the ‘normal’s in my life though.
Personally I just want to lounge by the pool. Hence my lack of fitness for life.