In my observation, a person with average native faculties in a given activity make themselves top 95th percentile of the general population in that activity, with dedicated and sustained practice. This applies to most specific skills - violin playing, chess, calculus, computer programming, golf, basketball, quarterbacking, painting, etc. Of course, the reason for this is the typical person in the population has not dedicated that much practice time to a given specific skill. You may be a great natural athlete, but if you have not spent at least some time learning throwing mechanics, a mediocre athlete who has practiced will be able to throw a better spiral.

However, it does not follow that "everyone can be a computer programmer for Google" or "everyone can be a professional quarterback." If you want to make it to a high-level in a high paying or high status field, you must compete against other people who are also practicing really hard and who also have great natural talent.

Personally, I have around natural athletic ability. I play flag football, and am likely in the top 95th percentile of QB ability. When I throw the ball around with friends at a BBQ, I can hit people in stride with tight spirals. But I could never, ever be a pro-QB, or even a QB in a competitive amateur league. My body simply does not have the appropriate build, and I simply cannot build the muscle strength to make the passes needed to be a great QB.

On the flip side, I have always had an innate knack for cognitive problems, I was always that guy in math class who got A's despite barely doing homework and not studying for tests. Now another person could also get A's in that class with only mediocre natural talent by studying very hard. They might think that, "Hey, I've worked hard, I got A's, I can do anything, I can get a job at Google some day." But if they go into the most cognitively demanding career, they will find themselves competing against the most naturally talented people, who also now have a financial incentive to work extremely hard, and the less naturally talented people will simply not be able to compete.

I find it unfortunate and self-serving, that so there are so many commentators and intellectuals, who are above average cognitively and (likely) mediocre athletically, who assume that the other people's failings at cognitive skills are due to lack of practice or lack of sufficient schooling. Meanwhile they assume their own lack of athletic ability is due to accidents of birth.

That said, it can be very difficult to determine if your having difficultly in a subject is really due to innate talent or due to lack of practice. When I took an intro computer science course, I noticed the professor was a completely horrible teacher (and lectures are generally a horrible way to teach math, computer science or any technical subject). The textbook sucked too. The people who did well in that class already had been programming on their own during high school. The people taking the class expecting it to be an actual introductory course, who expected that if you just followed the lectures and textbooks that you would know how to do the assignment, ended up doing very poorly. Even if they worked very hard, their total hours dedicated to understanding computer science was far below that of fellow classmates.