My belief is yes and no. Like many biological things it's both nurture and nature.

Many people think that the way they act is their "personality", when it seems more accurate that they have feelings/urges/likes/dislikes that manifest in a certain way and don't know any other way to act.

And because they might not have known a "them" where they were able to channel those urges in another direction (because they're young, or never tried, or have never seen an example at home to follow because their family is shitty or out of control) they think that manifestation IS their personality and is completely out of their control. Which becomes a self-fulfilling prophecy, because if you think something can never change you won't even try, and then it CERTAINLY won't change.

Changing how your own urges manifest is within your power. It's not always easy, but it is within your power. (Mental illnesses do make it harder, as mental illness often messes with things like emotional control or executive function, both of which are helpful to have when changing how you react to things. But I have known people with mental illnesses who made an effort to try, and those who did not, and even then there's a difference when it comes to actually "trying", and even with mental illness those who try and learn and grow get further than those who do not...although it does not magically "cure" the illness.)

Basically, it's possible to skill up when it comes to self-awareness, emotional control, and even understanding what is and isn't a threat, and all those things change how various aspects of your personality manifest in the real world.

But, beneath that, there are "the big five" personality traits that seem "real" to the extent that science pursuing investigation into them. Those are:

* Openness to experience (includes aspects such as intellectual curiosity and creative imagination)
* Conscientiousness (organization, productiveness, responsibility)
* Extroversion (sociability, assertiveness; its opposite is Introversion)
* Agreeableness (compassion, respectfulness, trust in others)
* Neuroticism (tendencies toward anxiety and depression)

( https://www.psychologytoday.com/us/basics/big-5-personality-traits )

People who are interested in and have the drive towards self-improvement can gain and practice skills that help them redirect behavior and urges within themselves that they don't like. For example, maybe someone who gets angry really easily starts to recognize when they're feeling like that, and instead of shouting at others and ruining relationships, they go out running and get some exercise. Or, the reverse--someone who never stands up for themselves learns to.

I don't think it'll eradicate some tendency towards certain personality traits--but it can bring them under control so you stop holding yourself back due to it.

I have a friend, and he and I have made opposite journeys when it comes to anger. He's had to learn how to channel it back, tone it down. I've had to learn that my anger is "okay" to express sometimes. We were opposite ends of the spectrum and have each made progress more towards the center. We still default back to what seems our "inborn personality", but we also have a lot of times when we act different ways because we've chosen to and have better control over ourselves. And when you do that all the time? Well, it's a pattern, and it's "you" just as much as anything is.

I'm generally soft-spoken IRL, and quiet, and a loner. But I'm also a writer, and because I wanted to progress in that Craft, I learned to write and "speak" with authority, because a writer who quivers and wrings their hands every other sentence and seems to lack confidence isn't going to be interesting or compelling to read.

This is not a natural talent of mine--but I worked on it. And I worked. And I worked. And I did eventually gain skill in "sounding" confident in myself--to the extent it sometimes causes trouble because people expect one thing when they've read my writing, but get someone who is much quieter and much less talkative in person. Obviously, I have not put the same work into my in-person speech, and have not worked on dispelling my wallflower status there, but having seen how things turned around for me in writing because I kept trying, I imagine I could turn it around in person if I wanted to.

...IF I wanted to.

"Wanting" to change is probably the biggest thing when it comes to self-improvement. If you don't like who you are and want to change it, it's really important to cultivate that desire, because that DESIRE to change is the thing that keeps you going through the hard, frustrating parts of changing and gaining skills in self-understanding and self-control.