Earlier quoted context omitted.
It's also a mistake to think that people are static. We can improve ourselves through the expenditure of effort. The reality is like the parent said: there are limits to everybody's abilities, but you'll probably have to work hard as hell to reach yours (not targeting you personally, the general case "you"). If you believe that your present abilities are all you'll ever have then you're wasting what could be tremendo…
Who said anything about not improving, the parent comment believes the ADHD sufferer is simply not working hard enough. He's trying to show him where his bootstraps are.
From my perspective it's a positive message, not finger wagging at the impaired.