Two things come to mind:
(1) Neurotypical people often don’t realize that people with ADHD have hyperfocus times as well as scattered-focus times. Thus, neurotypical people (e.g., parents (or bosses)) ask with frustration and anger, “how can you have ADHD?! I’ve seen you sit for hours playing a video game (or reading a reference book).” They don’t understand that ADHD is a challenge of attention control, rather than a “lack of attention ability.”
(2) Neurotypical people don’t notice that smart people with ADHD often live with a lot of shame because they “know” that they “should” be achieving more and doing better because they’re smart and have the ability to do high-quality work. A person with ADHD might be extremely productive one afternoon and feel like they should be that productive all the time. A student with ADHD might be told by a teacher or parent, “you’re so smart — you shouldn’t be making such bad grades,” because the teacher or parent doesn’t realize the challenges that the student has with things like remembering due dates or following detailed directions.
I wrote this post as a response to a question on Quora.com. See here for more responses: https://www.quora.com/What-are-some-of-the-biggest-unknown-ADHD-struggles-neurotypical-people-dont-think-know-about