One of the life principles that I believe is core to overall happiness and prevents mental/physical decline is to simply not allow yourself to peak. There shall be NO moment in life when you feel like you’ve reached the top. A daily mantra should be, “my best days are ahead”.
Even if you’ve reached enormous success at a very young age, way better than the average person who’s 20 years ahead of you, you have to believe that the best days are ahead. Everyday pursuits become meaningless once you believe you’re at the top.
So many people I know achieved their peak at high school, college, or early in their careers. The gradual decline after that can be miserable, even if you remain way above 99.9% of people. After all as Tim Urban writes, Happiness = Expectations - Reality. When your expectations are high, so are your standards for happiness.
The most fulfilling way to live life, in my opinion, is to always have the next goal to reach, even if it’s an arbitrary one. And when you somehow reach that, push the goal post even further.
That being said, don’t mistake setbacks for decline. Growth is not linear. Failures happen, and are necessary towards long term success. Just remember, your best days are ahead.