I could build a house. With zero experience you can find a job in house building as they will pay you to learn on the job (depending on the economy you might or might not be able to find such a job today, in good years they will hire anyone who isn't disabled - but there are bad years). Many people who have never had a construction job build their own house (only a tiny %, but that is still a lot of people)
I suppose I could work on a cancer cure. However since I don't have a background in biology I would have to pay for several years of school to learn the required skills. Those classes are hard and there is no guarantee I will pass (I have an engineering degree, so my odds of passing should be above average).
Depends. In rural areas the only part you can't do the power company will in five minutes. In other places only a licensed electrician is allowed to touch wires and do you can do much less
