"What we have here is a failure to communicate", Boss to Paul Newman in "Cool Hand Luke." I lost you on Def 1 and 2 theory. Have you ever had to do something difficult?
The GAO ( government accounting office) says by far it is auto mechanic. It is interdisciplinary , constantly changing educational target. Capitalization is very high when compared to the median income also.
Yes if you decide to work for one of the big guns it requires a lot of hustle and pressure. You have the flat-rate manual and if you don't beat that or if you get to many come-backs you are held accountable. Like a lot of jobs that require hustle it works for the guys who love it and are good at it; even they can get stressed at the unrelenting get 'em out demands. And the constant educational demands are difficult especially when you get older. But yes they can make a good buck at it now.