But it's not immutable. I've seen stuff about me change that I thought was really important and deeply ingrained, and I have seen stuff stick around that I thought didn't matter.
I can influence what sticks around and what changes. Here's where [the] metaphor of a sculpting medium fits, for me -- some things are hard to change, take lots of energy and thought. Some things are easy to change. Some things I'm trying to change need special treatment before they can change (like heating or moistening changes the workability of some media) or time to cure and solidify once I'm doing with the shaping part. Some changes have unpredictable effects -- I'll have shaped something and set it to cure and it just cracks and crumbles. And some sculptures don't have the proper structure, so they just fall apart when subjected to everyday forces. (I am terrible at building lego sculptures.)
And sometimes what's best is to sit and look at the medium for a long long time because you want to create the kind of sculpture that still expresses the soul of the medium, more than you want to work the medium into something that it doesn't look like on its own. (When I see watercolors that look like oil paintings I'm impressed but not in the same way as when I see watercolors that are expressing something that only the medium of watercolors is really good at expressing.)