Answer:
If you were to make a career out of your hobby, you'd need to learn how it actually works. Writers have to learn how books are published, singers need to learn how the music business functions, and dancers need to learn what their expectations are. If you made a career out of your hobby you would most likely need to go to a school. Sure, there are people who do their hobby without having gone to actual training but you almost always need it.
The type of training most people take is when they go to college. They more often than not go through a type of school at least similar to college. Hopefully if you're good at what you do, you'll get into a good school and that will definitely boost your chances. You need, for lack of a better word, experience in your field. If you needed to write a book but didn't know how to write, if you were to play the guitar but had never played one in your life, or were to paint without ever picking up a paintbrush beforehand, you wouldn't make it too far. That is why you need training.
(Sorry if this was long!)