In some ways, all people see themselves as the main characters of their own story. You are the focus of your own life while everyone else is a supporting character. Everything that happens to you is most important to you, not to anyone else involved. You see things primarily through your own eyes, not through the eyes of others. You are your own main character.
This is the middle ground. It can, of course, go to either extreme. The first extreme is both obvious and common. Sometimes, someone is so wrapped up in herself that she forgets the importance of everyone around her. The other side, though, is when someone is so focused on other people - on the supporting characters - that she forgets she is her own protagonist. FOMO...Fear Of Missing Out...where does that even come from? Missing out from what, exactly? If you are the focus of your own life, you should never be missing out from anything! Right? If it didn't happen to you, it isn't part of your storyline. Other people can miss out from events in your life, but you can't. After all, it's your life; it's your story.
And then there are different kind of stories. There are the kind where the supporting characters are extremely involved in the storyline. They form close relationships with the main character (aka - you) and help her through whatever obstacles come her way. But then there are the kind of stories where the main character has to learn things on her own. She has to deal with situations using her own reason, intellect, cleverness, and strength. Sometimes the main character can't receive any help at all. Sometimes, only minimal help. Sometimes, certain stories are so focused on the main character, any other characters are only mentioned in passing. But what a lonely, difficult trial that must be for the main character. And yet what better way to measure her own strength?
And, sometimes, I like to abandon this entire life-is-a-story theory and just live it instead of thinking too much. Otherwise I might get a headache.