Every time you say “that’s just how I am,” you lock a door you might want open later.

Describing yourself as fixed is comfortable because it ends the conversation and removes the obligation to try. The problem is that the description tends to become accurate, since you stop collecting evidence against it. Traits you call permanent are usually habits with a long history. Naming them as permanent is a choice, not an observation.

Catch the phrase the next time it comes out of your mouth and rewrite it as a sentence with time in it. Not shy, but not practiced at this yet. Then do one small thing that a person with the other description would do.