Vox and I had a brief chat recently and the topic of complicated music came up. As everyone knows, Vox is not a trained musician and admits he can barely play an instrument, yet he was a top 40 Billboard recording artist in the early 90's. Contrast that to a formally educated musician who works at Starbucks. How is this possible?
We got on this topic because I mentioned a time that an asset I had written for a company was rejected because it was too complicated. Vox recounted his experience with musicians who wrote songs that only other musicians would enjoy, and I explained - glibly - that was why I quit jazz. In my opinion the hardest skill for a musician to learn is how to hear music as it sounds to non-musicians. Vox wanted more: "If someone is skilled, how can he not know that? I know how to imitate writers, why is this tough for musicians?"
I was able to give a partial answer: there is in music a similar dichotomy as exists in persuasion, namely, between music that is dialectically correct and music that is rhetorically effective. It's a different set of skills. There's what you learn eight hours a day in a practice room, and there's what you learn in front of an audience.
Only half satisfied with that answer, I want to revisit my original assertion: "the hardest skill for a musician to learn is to hear how music sounds to non-musicians." Why is this so?
One reason might be is that music is perceptual. Most people cannot focus their attention on each separate element. To make music at a high level of skill, however, you need to be able to hear each element in isolation. Once you can, however, it's easy to forget that a non-musician can't. The next thing you know you're creating music for people that can only hear it the way you do.
As your ears become more refined you must not be lose track of the big picture. Mixing helps in this area, by guiding the listener's attention from foreground element to foreground element.
In music the meaning of a sound is different depending on what surrounds it. This differs from language where the meaning of a word has finite definitions from context to context. In music a single sound has infinite potential meanings - except for when it doesn't. There is no such thing as a musical dictionary. A minor chord in the key of E mean somber, unless it means groovy, upbeat, or something else. To compound this our sense of how context functions changes depending on what we've been exposed to. Musicians, by expanding their knowledge in pursuit of their craft, are exposed to more possibilities, and can't always remember how Green Day used to feel before being exposed to Ligeti. It becomes difficult to express yourself honestly in a simpler idiom.
Sometimes musicians have bad educations. My relationship with music theory is akin to Vox's with economic theory. After much questioning, I concluded that most of what they teach undergrads is worse than useless. The fundamental problem is that harmony is placed at the center of the theory curriculum and it's the least important element of music. No one has created an adequate theory of rhythm, which is the basis of harmony, so it's not formally taught in school.
Western functional harmony is fundamentally a cycle of three types of chords: tonic, predominant, dominant - and back to tonic. To identify where the cycle starts you need to analyze the large scale rhythm. Most harmony textbooks acknowledge this, but then say "but it's beyond the purview of this book to analyze rhythm." It follows that a proper undergrad music theory curriculum would start with a theory of rhythm, with the aim of teaching students how to formally recognize the beginning of a rhythmic cycle, and only then move on to harmony. Instead, the vast majority of music curricula do not offer even a single course on rhythm.
There's very little out there in terms of formal rhythmic analysis. What little you find usually presents itself as an introduction to a field that has only begun to be explored - and this has been going on for decades. So it's possible for a music student to finish school thinking he understands harmony because he's learned everything there is to know ahout Neapolitan 6th, false cadences, and set theory. But he's never studied rhythm beyond a professor offhandedly telling him "well, you just kind of have to feel it." So he becomes one of Nicholas Taleb's "Intellectual-Yet-Idiots." He can speak for hours on a topic without realizing the foundation is faulty.
Contrast that to a naturally curious autodidact making Hip-hop beats at home. Without a teacher to distract him with a foundationless theory of harmony, he gets a ten year head start studying rhythm, and when he's ready to use more interesting chords, they are anchored in a solid rhythmic foundation.
There is also the aspect of finding the right symbols to connect with your audience. You can't learn that in a practice room. You learn that on a stage or whenever non-musicians candidly respond to your music. There's a genius that knows what symbols resonate with culture in a particular moment in time. It has something to do with freshness, timing, context, and other intangibles. It's a skill more like public speaking than writing. It's has more to do with fashion than architecture. All of the musical elements, rhythm, timbre, space, harmony - all these do is add up to a gesture. A formal music education can teach you how these elements add up to a gesture - they can form a coherent statement - but to know how they whether they resonate with an audience, you have to interact with one.
Formal music education isn't necessary to make music that people will pay for. All you need for that is curiosity and an audience. Creative longevity, however, requires wide exposure to many styles, and formal education can help with that. Many one hit wonders make a splash, but then run out of gas because they can't do anything else. You'll find that the truly great musicians have spent a lot of time in front of audiences and have also investigated many styles of music beyond the ones they perform.