I’ve always believed people have unlimited potential for learning music. If they put the time in to really develop themselves anything is possible. For years I’ve conquered limitations within my own musical development and have helped my piano students consistently do the same for themselves.
The problem that comes in is that most people aren't focused enough to actually put in time consistently for the long haul. So, instead of actually exploring their own talent deeply and completely they'll take the easy path. They'll "practice" or at least try to play their instrument for a few months. Of course most of this time is unfocused and unstructured. After they run into they're first plateau they immediately feel like they have found their final stopping point. They'll say things like, " I just don't have it" or " I don't have any talent" or "that person is just born with it and I'm not" or "I'm just not a natural".
Becoming an expert at an instrument is really about finding ways to navigate past plateaus in your development. This process repeats itself over and over and that's where the real talent and skill is built. The pyschologist K. Anders Erricson has done some amazing research into the field of expertise. One of Erricson’s main points is that it takes 10,000 hours of study to become a true master or virtuoso at a skill. The vast majority of people I encounter who limit their own potential haven't even put in 500 hours of study yet. How can you make such a broad generalizations of human potential if you've not put in anywhere near the time necessary for deep skill building?