Mastery level: to know everything there is to possibly know about a given subject without the need of an outside reference.
True, you are on the mark with my point. In these times, mastering a “field” is an impossible task. There are too many variations, spin-offs, sub-categories, etc. within every field, that it would be impossible to master the field as a whole. At least in the technical world.
I remember when I was younger, in my early 20s, I knew a man that was the master when it came to oil field pumping units. There was never an issue he couldn’t resolve inside of a day at most. (Pending part availability.) In that era, these units had changed very little in the past 100 years. So, mastering them was accomplished by years of experience working on them. But a mastery was achievable.
Those units still have changed very little in the recent 50 years. So, a mastery of them is still within one’s grasp, provided you can stay with a company (or at least in that workforce) for a number of years. Much like the umbrella which has had little to no changes in the past 3,500 years. Save for the cosmetics and a few mechanical improvements.
To apply that level of mastery to today’s computer driven world would be an impossible task.
In my humble opinion.