A piano teacher my junior year of high school had me do exercises I didn't understand. A teacher in my college audition heard the result of those lessons and started me down another path of exercises. Essentially, the one teacher had communicated certain skills through me to the next teacher without my knowledge.

During one particular lesson my junior year of college, everything clicked and I began to play a melody with more control and direction. It was only at that moment that I could hear and feel the result of those exercises.

Furthermore, that teacher later speculated about the lessons my previous teacher had taught me. That speculation lined up pretty well with what I remembered of the exercises she gave me. And it was only then that I understood the efficacy of those lessons toward connecting a melodic line on the piano.

That's about 4 1/2 years and two mentors setting me toward developing a skill (in addition to others, granted), the process of which I didn't really understand for another half year after that.

And that's the best case of someone willing to do what seems like arbitrary work, and lacking the skills at the time to rationalize persuasive reasons to avoid doing that work. In my experience adult students are experts at talking themselves into the skills they think they already have, and talking themselves out of the will to learn new ones.

So without a decent mentor I'd speculate most people are hopelessly incompetent at assessing their circle of competence. Or at least they are if we widen the circle from "getting ahead in business" to "life."