Feeling good about your life is all about having the right self delusions.
Feeling bad about your life is all about having the wrong self delusions.
We all tell ourselves stories about who we are. These stories frame our experiences in certain ways. One person's exciting life is another person's wasted life.
As you get closer to 40, the question "Who are you?" gets increasingly difficult to answer because—surprise surprise—you have turned out to be a very ordinary person in many respects.
There's this phase of your life from about 15 to 25 where you experiment. You don't think you're experimenting, though. You think you've discovered that you're a multifaceted individual with great ambitions. In the middle of this, you try to keep your life together, and it often gets messy.
In the end, you discover that you're still pretty much the person you were before you hit puberty, except you are now more mature and experienced.