The well-defined output to a very limited set of skills is the sudden stop that will kill you when you crash the airplane...lol

It is not funny, as it happens about once a week. After the NTSB investigates the "accident," the cause is generally always the same: "pilot error."

If "well-defined output" means one song someone learned by some method, that person would be highly unlikely to be able to articulate that song twice the same if there was any level of complexety.

What you get with that one song that you learned by whatever method is plausible music at best. Even untrained ears can hear the lack of proficiency.

There is no exact definition of correct finger position on a piano. There are excepted "norms" that apply to people whose hands are big enough to produce that fingering. Different fingerings, correct or incorrect, produce different sounds on the piano.

It would be doubtful that anyone who only spent the time needed to learn one song of any complexity could play it like the original.

Obviously, one does not need to study and practice for hundreds of hours to learn to play the three chord 1, 4, and 5 in the C key at 60 BPM.

Professional musicians get better year after year on their way to becoming great musicians.

You can not even hear the mistakes you are making when you start out.

Most of us play music because it is something we like to do, and we have no intention of becoming highly proficient musicians. We mostly only get good enough to get by if we are lucky. A huge number of guitars and pianos" get shoved in the corner, never to be used again." Next time you go to someone's house and you see a piano sitting there, ask them to play it.

I know many musicians who "think" they can play a lot of songs, but they can not play a single one correctly. They have limited hearing, no reading skills, and no writing skills and, therefore, are seriously unable to communicate or be communicated to by other musicians.

Welcome to the typical bar band, let's get drunk, have some fun, and play Mustang Sally.

There are other musicians who have worked diligently and gone to school to get an education. They have worked thousands of hours to try to perfect their craft. Many of those people are icons we look up to, and some are virtually unknown.

Billy

“Amazing! I’ll be working with Jaco Pastorius, Charlie Parker, Art Tatum, and Buddy Rich, and you’re telling me it’s not that great of a gig?
“Well…” Saint Peter, hesitated, “God’s got this girlfriend who thinks she can sing…”