Over the course of our childhoods we experiment with personality, and discover the elements that allow us to have stable and satisfying dealings with the world. We may cultivate several different personalities— each of them the real us in some respect.
Of course there are many elements of personality that are autonomic or otherwise habitual. That doesn’t mean personality is somehow not real.
A con artist or an actor can don a fake personality, but all that means is they are telling a kind of systemic lie to the world. This requires a lot of energy to maintain. Your real personality is that which minimizes required energy.
This is not the same thing as what you show to the world. "What you show to the world" implies that personality is merely a veil that covers stuff. It's not a veil at all. It's an interface. The "real you" that acts through this interface is beyond words, personality is not "showing it" because it can't be shown, but rather mediating it via actions.
Some of my language patterns come from watching and interacting with my stepfather. He was big man with a loud voice and an iron work ethic. I didn't get along with him when I was a kid-- in fact had to leave home after threatening his life-- but as I became a man I decided that I was going to force the world NOT TO IGNORE ME. So I tried on his tough-talking, Navy veteran persona and found that it fit me. Now I'm 275 pounds and have a loud voice and I know how to use it.
I'm not PRETENDING to be something I'm not. I am using a style of interaction that fits the "real me." I AM a man, and I SPEAK as a man. And my template for manliness is my stepfather. At the same time I'm also an intellectual, and I adopted certain patterns from my biological father. I also borrowed patterns from the writings of C.S. Lewis and Tolkein. Sometimes I channel Gandalf and sometimes Boromir.
Children have become adults in this way since a million years ago. There's nothing false about it.