How about this though (-has this happened to anyone else?
I've revisited a few projects that relied on said 'endless tweaks and refinements' - say hearing it after a year or two, thinking 'I can fix that now! -only to open it up and find (remember-!) all the very real reasons I was forced to make those 'poor decisions' in the first place?
You couldn't lay it out.. and didn't lay it out -'cause the track didn't lay it down.
Yep, I know that syndrome well.
I *still* have tracks that I got from a musician friend of mine for mixing some 10 years ago or so. He recorded them on an old Otari 8-track open reel tape with heads that had seen better days, and drum tracks of dubious quality. But it was one of those projects where performance lightning was caught in a bottle on the guitar tracks. There's moments in that song that just come together like magic. Even though the overall tracking quality is not quite there, I have hung on to those tracks all this time because the content is so damn promising.
I have on a couple of different occasions in my spare time over the years gone back to those tracks and tried re-mixing them, applying some new tricks and techniques that I have learned since then, using fresh ears, and also newer, higher-quality gear and plugs that I didn't have 10 years ago. Every re-mix I tried either failed miserably compared to the original, or came out *different* than the original mix, but not really all that much better to justify the extra hours I had put into it.
It turned out that my instincts were pretty much on target the first time around, but there just wasn't really that much more blood that could be squeezed out of the tracks I had to work with.
You're right, it's very tough lesson to learn, and you're even righter in that much of it does have to do with one's experience level at the time. Working on a mix over and over for hours and days indicates on a less-than-obvious level a lack of confidence on the part of the engineer. They just keep thinking "this HAS to sound better than this, there just must be something *I'M* missing or doing wrong.
Sometimes they might be partially right, but they are almost never completely right when they think that, IMHO. Sure, sometimes all it takes is a parametric sweep technique on one track that the newb hasn't learned yet in order for the mix to jump from "mediocre" to "pretty good", but rarely, if ever, will that be "the missing ingredient" that takes it from "pretty good" to "THAT"S what I'm talking about!"

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But the more experience one has, and the more confidence they have - sometimes it only takes one great-sounding mix to give it to them - the easier it is to recognize and admit that sometimes the tracks just do not and will not sound the way we would like them to, no matter how we try to cajole them.
G.