I'm approaching 30 years of professional work and still feel this way. I've found some people are like this, and others aren't. Those who aren't tend to not progress as far.
> embarrassed to check in a pile of slop
I feel that's the bare minimum a junior should be asking. the "this is useful" or "this is slop" will come with experience, but you need to at least be able to explain what's going on.
the transition to mid and senior goes when you can start to quantify other aspects of the code. Like performance, how widespread a change affects the codebase at large, the input/outputs expected, and the overall correctness based on the language. Balancing those parameters and using it to accurately estimate a project scope is when you're really thinking like a senior.
early on when I was doing iOS development I learned that "m34" was the magic trick to make flipping a view around have a nice perspective effect, and I didn't know what "m34" actually meant but I definitely knew what the effect of the line of code that mutated it was...
Googling on it now seems like a common experience for early iOS developers :)
https://stackoverflow.com/questions/14261180/need-better-and...
https://stackoverflow.com/questions/3881446/meaning-of-m34-o...
I keep hearing this and find it utterly perplexing.
As a junior, desperate to prove that I could hang in this world, I'd comb over my PRs obsessively. I viewed each one as a showcase of my abilities. If a senior had ever pointed at a line of code and asked "what does this do?" If I'd ever answered "I don't know," I would've been mortified.
I don't want to shake my fist at a cloud, but I have to ask genuinely (not rhetorically): do these kids not have any shame at all? Are they not the slightest bit embarrassed to check in a pile of slop? I just want to understand.