“Fake it ‘til you make it”. By choosing behavior that may not feel ‘natural’ but is more like the person you want to become, you will progressively integrate those behaviors into your personality.
My personal experience comes from have zero self-esteem, and even some self-loathing resulting from childhood abuse. I was a horrible under-acheiver and painfully shy. In my late 20s, as I was starting a new job and building a career. I had finished Grad School and given birth to my son a few years before. I found a therapist I really liked, and one of the things she suggested was the above theory.
So I observed people around me, and their behaviors. Those qualities which I found admirable were the ones I tried to emulate. I wasn’t imitating them—I watched how they could stand up for themselves to an authority figure and remain poised and dignified (for example), and then I’d consider times that I’d had to deal with confrontation and imagine what I could do differently to avoid getting flustered. That’s been the toughest challenge, so that’s why it makes a good example.
At first, it did feel awkward; but as I persisted, I became more comfortable with those behaviors and they are now a part of who I am. When I meet people now and tell them how I was as a teen and young adult, they seem genuinely surprised. I am no social butterfly, because I have realized that I don’t want to be that way. A new aquaintance described me as a “sociable introvert”, which suits me well. I am at ease in social situations and confident meeting new people.
Pretending to have confidence gave me practice at behaving like a confident person, until the point I became comfortable with being confident. I grew up believing that I was ugly and stupid, and undeserving of happiness or success. Logically, I knew that to be untrue, but that didn’t change how I felt about myself. So by changing my behavior, I was able to challenge and change those beliefs about myself.
I hope this makes sense, and that it relates to your question the way I interpreted it.