"Being a musician", maybe?
It needs talent, which arbitrary amount of work can't compensate. Talent may result from genes, but it could be a matter of culture or of early personal development too.
The social group has a very strong influence. Jews and Gypsies are extremely over-represented among the best violinists, Korean women presently too. Whether this results from genes or culture, nobody knows.
Musical talent passes little from parents to children. The general feeling is that exposure of the children to music suffices to explain that more children of musician parents become musicians themselves.
And while playing one instrument helps a lot to learn an other one, pupils are rather gifted for one specific instrument, more than for music in general.