I believe it is similar to music theory or color theory. You can be creative and make up your own expressions, but there are principles and fundamentals that are operative in what you are doing, and once you understand those principles and fundamentals, your expressions become more "effective" so to speak, in conveying your intended message to the audience.
Just like learning a new instrument, you learn the basics first, how to hold it, how to clean and care for it, and then you pick up some really basic songs to start with just to get the hang of it, and then you progress to something more challenging to practice new techniques you want to learn as you go. This half of the process is called "musicianship" where you put the practice in to actually learn from hands-on experience.
The other half is music theory. You study the timing, the notation, the fundamentals of WHY certain chords sound pleasant to the ear, and WHY music has a certain structure to it. That stuff is academic, but knowing it gives you insights when it comes to your practice so you actually understand WHY you do the things that you do. You become aware of not just WHAT and HOW to make music, but WHY. And that's really important in the long term if you ever want to go beyond imitating other musicians.
You put the two together and that's how you become a great artist, in any kind of art, whether it's music, dance, sculpture, poetry, you name it. There's the practice, and there's the study, but it's not just about how well you can replicate what's been done before. That's only half of it. The other half is BEING the one who wrote the songs you're learning, who discovered the rules you're applying. Become one of these people yourself. That requires a leap of faith you have to make on your own whenever you're ready.