If you have never been an immigrant, you’d have little reason to understand the corresponding regulation. Many simply imagine them to make sense, but in fact they don’t. John Oliver explained it quite brilliantly recently:
I wish it’s easy to tell people what I do. The fact is, I am genuinely interested in different things. I have studied composition for my undergrad and graduate degree. I have been playing taiko for over 10 years. I have professionally record classical music. I have tuned pianos in a university. So, each of these could be some sort of a profession, just not my only one. To me, they all compliment each other.