Self-absorption, or solipsism, is defined roughly as "wanting to believe that you are the center of the universe" (you'd have to want to believe it), and it's undeniably a Huge Thing in the present culture, because let's just admit it -- you either are or are never more than 10 feet from someone with the ego to secretly suspect that society is literally an elaborate Truman Show-style situation with themselves at the center (I'll go first and put my own hand up, although I have long stopped looking for the hidden camera in my bathroom mirror). But as comforting as it is to think that you're more real than everyone else, you're ironically screwing yourself over by believing you're the anointed protagonist of life's movie. A lot of us need to get over ourselves, in other words, and I'm sure you've noticed. I've mentioned before the romantic consequences (or lack thereof) of thinking that you're The One True Human, but here's a bunch of other self-sabotage that occurs when you're Truman.
#5. You Take Everything Personally
When you're the protagonist, everyone is talking to you. The pitfalls are many, from assuming a passerby on a headset phone is saying hello to you to being embittered for days when insulted online, because as the protagonist, everyone in the world knows everything about you and their insults must be taken directly to heart (plus you're all too ready to insult others, as other people's feelings aren't as real as yours, and thus a vicious cycle is born). That's the problem with thinking you're the Truman part of The Truman Show -- you drastically overestimate how much others are focused on you in daily life, and always to your detriment.
"I can't wear this shirt to the party, WHAT WILL PEOPLE THINK?!" Well, they'll probably think "Hey, look at that shirt, it's- OH GOD THERE'S SUSAN WHY CAN'T I BUILD THE COURAGE TO MAKE A MOVE? WHY CAN'T I MEANINGFULLY EVOLVE BEYOND WHO I WAS AT AGE 15?!" because other people are unsurprisingly focused on their own concerns. Like you are. And thus your own extreme self-focus makes you worry when you don't have to, and you deny yourself the borderline superpower of being able to wear almost anything -- a power that's granted by knowing that you're just a blip on other people's mental radar and effectively invisible to the vicious judgment that they reserve mostly for themselves. Like you do.
#4. You Fucking Bother Everyone
When you're the protagonist, nothing exists unless you can see it, because it's all there to serve you. Much like in a 3D video game where, to save on processing power, only things adjacent to you are fully rendered. Others' discomfort doesn't exist unless you can see it. The problem is that others are not always going to show their discomfort to the one disturbing them, due to the often reasonable assumption that the kind of person who doesn't care about disturbing others is also likely to be the kind of person who'll wordlessly knife you for daring to ask them to turn down the volume.
You the protagonist are blasting the same fucking Smiths album on repeat until 4 a.m. and that's entirely justified because you by default get special dispensation -- it was a rough week and you deserve it, and if the downstairs neighbors were bothered by it they'd say something. Except they wouldn't, they'll just spread word of their Asshole Neighbor who is incapable of recognizing others' existence. "B-but I'm not an asshole," you stammer, taking the insult personally. Except this time you are, because assholes are exclusively people who have to be told how others might be feeling and who think they get special dispensation to do anything. If you're not questioning your behavior, that means everyone else is. Behind your back. RIGHT NOW! It is of course true that some people missed the memo that the finest thing a person can do is build social connections and make life easier for others, and they simply don't care if others like them. Those people are wrong, and we are to draw sport from their folly.
#3. You Guarantee That You'll Fuck Up
You never question your own behavior because the protagonist is by definition infallible. Yeah, there'll be the obligatory scene with a dark night of the soul, but the movie is about The Hero, so whatever he or she ends up doing will be the story of how good triumphed over evil. The problem is that in reality nobody is always right, and being afraid of looking bad or simply assuming you can't be wrong is the one way to guarantee that you will be. If it's unthinkable that you could drive off the road, why would you ever keep your hands on the wheel?
You can even see this with entire countries -- ones that have long had good reputations and are therefore clearly incapable of doing wrong. It's unthinkable that they could, so when those in power consequently start fucking up beyond the ability of instruments to measure, they don't acknowledge the need for a national discussion because perfect people and countries don't make worryingly sinister mistakes -- they make correct decisions. They stay the course, and then eventually nobody can remember why they used to have such a good reputation. But don't bother pointing it out to your leaders -- they hadn't noticed. Despite being perfect.