Mastery would imply that you can do it all, and do it right, on any project, and there is just too much change and evolution for that to ever be true.
My goal is simply that I continue to improve.
Doesn't matter how much time/effort I expend, there is just no way to keep up to date with every moving piece in our industry (from hardware, to firmware, to software, to laws, to programming languages, to cryptography/security, to web standards, to multimedia standards/codecs, to physics etc). It seems like every single action that we take comes with trade-offs and that we can never make an ultimate good choice - that choice is only valid for a short time before it's trade-off gets triggered.
A carpenter has a set of tools. He has a set of materials. He has a set of blueprints/techniques. He can consistently build table with x qualities. When he is done with the table, it is done. He doesn't have to spend all of his time relearning how to build tables over and over, and for old tables to quickly self-destruct if he stops baby-sitting them. Or for some 12 year old carpenter in Russia to cause his table's wood to rot.
Every year that passes by, humans accumulate more and more knowledge. It would be impossible for a few individuals to know everything as their time in this life is limited. Thus we get forced to specialize, else we can get pulled into the general knowledge stream which can be overwhelming.
I've both seen and written code like that, so it does exist. Like anyone one else I've also written code that causes future problems. I believe I'm at a point in my career (25 years in) where I now write more of the former than the latter.
For example: I know people who have been skateboarding for decades and are just barely OK at it. How you practice matters.
I think there is mastery, but only in knowing that there is no mastery.
"I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either." [Apology of Socrates, Henry Cary literal translation]
I also have trouble believing you've been coding for so long and can't take pride in any of the code you've previously written.
I think I do what I do pretty well. The folks I work with seem to like it.
When we interview people, we do so in such a way that we believe someone is capable of showing mastery of the field, where those who have been in the field a long time and agree with your philosophy here know that about all we can can hope to achieve is humility.
It also feels like this fundamental to why this field has not been able to mature to a point of being a profession in the same form as other fields - because while we can teach a lawyer the law and we can teach a doctor a particular way to perform a technique, software is all just a bit wet and sticky.
I take it one step further, I don't believe mastery exists, or rather we don't have a consistency on what mastery 'is'.
I prefer the saying something along the lines of "expertise* just means you get in more trouble when you do it wrong"
* Expertise is replaced with 'black belt' for martial art expertise
I play violin, and know and admire many masters. What makes them so good is fun to study and pursue because they are worth emulation.
But it's not some secret or hack. It's a million small things and a lot of feel.