I appreciate your response.
I'm 32 now, and I've had a long time to think about this question. Here's what I think is the answer:
I lack the focus over time which is required to build a deep knowledge or skill.
In other words, I get bored or frustrated quickly. Once bored, or frustrated, learning tapers off VERY quickly. I'm not a child prodigy, so learning anything takes focussed effort over time. The second it gets hard, or boring, my ability to stay on task diminishes rapidly.
It's not as simple as "grin and bear it", trust me I've tried. In college that's all I did. Grin, and bear the struggle. That's no way to learn. I need to be able to sit, fail, learn, sit, fail, learn, succeed, over and over and over. But for every sit, fail ... a frustration builds. Even the slightest frustration / anger, saps you of focus.
If it's not frustration/anger from struggling that derails me... It's sheer boredom. I can sit and read a boring book, for example. But after a few pages, I'll straight up forget what I was even reading. It's like my brain just goes offline whenever I encounter something boring. I have to stop, and re-read whatever it was I was reading.
That's truly what it comes down to. I can't sustain focus on something long enough (hours, days, weeks) to become really good at it.
For what it's worth - I've been prescribed and have taken adderal. It's a miracle for focus, but I HATE how it makes me feel. My heart rate jumps 10-15 bpm (from ~50 resting, to 60, or 65). I FEEL my heart beating harder, which is not pleasant. Then, hours later once the drug has worn off, I feel down... Depressed, and still my heart feels 'heavy'. Oh and that's on a "small" dose (5-10mg). I can't take the stuff.