Intuitive vs intellectual understanding, and aging
This is a pretty broad topic, and I'm only going to treat a small aspect of it here.
When I was younger, I really felt like I was invincible. Intellectually I knew this was ridiculous, but on some deep emotional level I really felt it. I was quite sure that if I just felt enough and expended enough effort I could survive or overcome almost anything. This of course was very naive, and I'm aware it's a pretty common experience. Kids think they're invincible. It used to annoy my when adults in my life told me that kids think they're invincible. Of course I knew that I wasn't invincible. Why did the adults keep suggesting otherwise? Of course as I got older I learned the truth. What I knew was not just a matter of strict factual knowledge. I felt like I was invincible and in some ways acted like I was invincible. Of course nothing corrects this like age. I'm sure there's a plainly obvious evolutionary psychology explanation here; when you're young it's time to strive and achieve: status, a mate, resources, etc. When you're older you must guard and maintain what you've gathered. Both phases of life require different strategies, and so those strategies must change if one is to be successful.
So as I've said, lots of people have observed that kids think they're invincible. What I don't see much of is the losing your sense that you're the center of the world. Similar to invincibility, it's easy when you're young to believe you're the center of the world. Intellectually you know for sure that you're not. You wouldn't admit to thinking this way. But, on some intuitive level, you feel it. (or at least I felt it -- maybe this experience isn't as common as I'm assuming) Your failures and successes feel huge, and feel important. Are you leaving for college from high school? It's a major event, a turning point in your life. Something people will acknowledge and remember. Did you get a new car? Everyone wants to hear about it and see it. Etc. When you're older changing jobs might have a similarly-large impact, but you're quite aware that no one really cares. Even if they do care, it's a very grounded and boring sort of caring. The (annoying) kids these days might call this "main character syndrome," although that term is kind of muddy and also just seems to mean "deeply arrogant and self-important in an oblivious way." I think this distinction matters; even a humble 17 year old is probably taking himself too seriously.
Again, I think there is probably a simple evolutionary psychology explanation here; your youth would have been when you would start staking out the status of your local hierarchy. And your status in your local hierarchy would have been somewhat fixed, so every advantage you could muster would be quite consequential. Now, people leave their hometown almost immediately after high school, and whatever they spend so much stress and time building up is mostly discarded. This process is repeated again from college to the workforce, except perhaps in elite circles where it really did matter who you went to college with and who you knew. That's probably an interesting topic for another post. It maps to bullying in a way that I don't think people really understand.
In any case, this youthful and ignorant sense that I was the center of the world did follow me into my 30s. Quite diminished, but still there. The only thing that finally killed it was having children. It was on life support after my first child and is well and fully dead after my second child. Intellectually, I don't think I've learned anything (about my sense of sense, ego, etc) that I didn't know before. It doesn't feel like I've come to some epiphany. This realization is purely intuitive, and it feels like it was forced on me. It feels like having children changed my internal emotional state on a biological level, and now post-hoc my mind is scrambling to make sense of it. Perhaps this is too has its own evolutionary psychology explanation: before you manage to build a family it helps to take yourself too seriously; you need every advantage you can get to accrue status, a mate, and wealth. Once you have children that perspective could be harmful to the kids; they need to come first and big ego doesn't help with that.
Or, maybe I'm just immature. (those two thoughts are also not mutually exclusive: I could have been slow to mature and also finally had some biological realization imposed on me) I'm fully aware that it's far too easy to make up some plausible sounding bullshit when invoking evolutionary psychology. I'm not claiming I have real scientific knowledge here. But, when I had my kids my over-inflated sense of importance was permanently damaged in a way that feels totally involuntary.