My husband (51) and son (14) both have ADHD and both present with this issue. Both have above normal intelligence (formally tested as well as reinforced by high academic performance). SO firstly, this is not an issue of not being smart enough. I think it has more to do with how the ADHD brain processes information. When the input is pure fact, they are phenomenal at recall and memory. The moment the input is somewhat ambiguous and requires interpretation/ extrapolation they have difficulty, primarily because when given a choice of possible interpretations, they tend to go with options that are less likely to be the choice of the average person. This is what makes them creative and unconventional but also creates issues because their unconventional interpretation is not what others expect. I also think the ADHD brain is “literal” and filling in the blanks is not intuitive. SO they need to keep asking questions to fill in all the gaps, rather than making inferences like neurotypicals to complete the picture.