Maturity, which absolutely can't be taught, has a lot to do with it. I read a couple of years ago that adolescence lasts (worldwide) to the age of about 34. Obviously some people grow out of it sooner and some later (maybe that's where mid-life crisis comes from). In any event, I can tell in my classes to a fairly accurate degree who's interested and who's not -- who will stay with audio and who won't. I can't say with any accuracy who will be a success as that depends upon too many factors.
In general, in any subject, 10% of the class really "gets" the subject and will pursue it successfully; the next 10% understand the material and will probably have some association with it afterward; the rest are up for grabs. Some of that remainder may "get it" later but most will drift away. Given that most will find something else to do eventually, it is *imperative* that students attend a liberal arts college and not a tech school. With a good, solid, general education these students can apply their skills to something else successfully.
Barry