great question. i'm an adult now but thinking back on when i struggled most, i would plan my words ahead more and have anxiety more before speaking but my core was always a boy who was extroverted. the extroversion still won out in the long run. all to say, if you are introverted, and introverted all throughout any sort of progress you've made over the years, then i would say it's likely just you :) also, i've been where you are before thinking something negative that i could not prove. ultimately, i think in such an uncertain frame of mind you gotta just say hey, maybe i am this way because of my stutter; maybe i'm not, but this is who i am