My story...
Got hired on entry level (ish, I was an operator among other things at a product shop previously) at a job shop. First months were broom pushing and cleaning and maintenance, eventually shadowed for a few months, and then got put on an older (80's) Matsuura, next to a guy in his mid-late 50's, I'll call him Bill.
The guy had worked in his dad's auto body shop for a while, and eventually went into the army Rangers. Got an honorable discharge after getting shot up on an extraction operation in the middle east. He had some definite PTSD, and refused any mental help from the VA since he didn't trust their methods (probably rightfully). He was one of those guys that did everything 100% and super competitive and intelligent. Pretty short temper though which gave him a lot of trouble. He had also ran a solo shop with 4 or 5 machines previously and seems to have done pretty decently until hitting cashflow issues.
The shop we worked at basically had him as a skilled guy, and whatever apprentice was there would be on the old matsuura doing simple stuff, mostly keyways, and have Bill help out and teach where possible. Pretty good system.
I, being the stupid 19 y/o kid, did plenty to piss him off, and I learned pretty quickly that "why are you doing it this way" can VERY easily be taken as "you're doing it wrong".
At one point, I was cleaning up, and used an old shop broom that we shared, to brush some chips off the table in the machine (after the coolant had dried so I figured it was fine. It was not). Got a good 5 minute cussing out for ruining a shop broom, which I deserved.
I took the point, and next morning on the way to work I stopped by home depot and bought a new one and put it next to the old one. A day or two later he asked where it came from and I mentioned I picked it up to replace the shop one, and after that it was gravy. Not just machining techniques of which he was an excellent teacher, but how the shop dynamics worked, and why one guy was doing well or another wasn't, and how he started his shop. He was the only guy I told when I got my own machine and he helped set it up, and helped out with advice for buying tooling and what kinds of jobs do go for or avoid up until I went full time and quit there.
I heard soon after from one of the other guys that he quit (mental stuff) and went elsewhere. I tried for a while to track him down but none of the contact methods I had worked, so he may have followed through on some of his stories and decided to go live off the grid somewhere. Apparently he owned a number of gold claims up in the Placer hills.