I have another acquaintance who's a musician (an actual musician, unlike me -- I'm just a programmer who likes playing the drums). The guy obviously had a lot of practice, especially as he graduated a famous music academy so he had to play the violin a lot.

That being said, he started taking violin lessons when he was 6, but by that time he could play it pretty well. Having realized that he can't remember the songs he was inventing, he even developed his own rudimentary notation system (when he was about four), with horizontal lines whose length indicated direction and a combination of dots and relative heights to indicate pitch relative to the first note of the song, so that he only had to remember where to start from. His violin technique was also remarkably good. When he started giving violin lessons himself, he struggled with understanding the first gripes of beginners a lot more than he'd expected. For instance, he never realized it takes so long to learn how to properly angle the bow when playing the second and third string of the violin (they're at almost equal height with respect to the base of the resonance box, so most beginners will unintentionally stroke both at the same time). Not only did he not remember having that problem, he literally never really imagined that someone could have that problem.

He's one of those people who does have an innate talent; there are a lot of techniques that he never learned, nor really "discovered" through an iterative process, he just figured out it would sound good if he did <something>, and it did. His brain was wired in a manner that's favourable to playing the violin and to music in general.

Needless to say, he still had to practice a lot -- he had to learn "proper" notation, he's constantly refining his rhythm and coordination, he had to learn how to play in an orchestra, and it's not like he could play any piece, no matter how difficult, from the very beginning. But there were things which his mind and his body could do without being taught, or which, at least, they discovered a lot more quickly than others did. They weren't enough to make him an orchestra-level musician from the moment he set his tiny three year-old hand on a violin, but they are certainly enough to set him apart from a lot of musicians of his age and experience.