Actually, I do agree that this number is kinda arbitrary and it of course depends on the field you want to become master in. But that doesn't matter, the import

Actually, I do agree that this number is kinda arbitrary and it of course depends on the field you want to become master in. But that doesn't matter, the important point is that you perform deliberate practice. If you look at any expert/master/virtuoso in a given field, you will notice that they did just that, the more complicated the field the more hours they put into it to master. You seem to tend to believe that virtuosos aren't made but born, ie nature vs. nurture. I think that practice plays a much more important role. That is, a natural disposition maybe be a necessary but not the sufficient condition. Really, read that book "Talent Code" I think it's better suited to get that point across. :)