Cleaning lady, construction worker, janitor, plumber, electrician, building inspector I could go on.

Full stack web development, growth hacking, lead generation/user acquisition, on- and offline marketing and entrepreneurship in general. I have half a dozen close friends who dropped out of high school and/or college and used their raw "ingenuity or shrewdness" rather than any learned skills in order to achieve enormous success (tens of millions of dollars). Some of them in Silicon Valley, but others in boring places and boring fields. In the past there were significant barriers to entry in many fields that required expensive, time consuming, often discriminatory pedigree to pass. These barriers have largely been destroyed over the last decade. The walls have been torn down and the ladders burned (much to the discomfort of those mid-climb), and they aren't coming back. Persistence and cleverness are the deadliest combination these days.