I can’t think of a single job/career that can’t be mastered with some ‘study at home’ and a spell as an intern.
I'm guessing that you have not finished either a B.S. or higher degree in the physical sciences or engineering and attempted a highly technical profession. As one who has done these things, I can tell you that my undergraduate and graduate studies prepared me in ways that home study and on the job training did not. I have never seen someone at the top of one of these fields without an advanced degree.
You guess wrong.