What careers can you think of that one can enter without needing any formal courses? What professional certifications, which lead to employment, can be obtained by independent learning?
Enlist in the military - You will learn everything you need to know after you are hired. Training starts on Day 1.
Do you mean learning "without formal courses", or do you mean "by independent learning" ? They aren't necessarily the same thing. For example, in several states it is still possible to qualify for the Bar Exam by apprenticeship, rather than through law school. So in those states, you can become a lawyer without "formal courses". However, this is not "independent learning", because you can't be an apprentice independently. You have to work under a practicing lawyer or judge, who is responsible for monitoring your progress. ***** Another example: in California, it is technically possible to qualify for a Professional Engineer's license without any formal coursework. But you would need to have lots of supervised work experience under a PE to qualify for the licensing exam. So while it's possible to get a PE certification without college, you can't do it completely independently. Again, it's more like an apprenticeship.