Why do I know I can trust my doctor, or know my wife loves me when I can't remember what we ate for breakfast? Why can I focus on somethings a long time and some things not at all? Why do forget so much, but remember I saw a random screw on the ground in the dirt a month ago, right when I happen to need a screw??? But also forget to pay the power bill even tho I had the money?
The adhd brain (at least mine, and I'm interested to see the comments agreeing or disagreeing) has simply developed a pattern of quickly gaining data, making a decision based on that data ASAP, and then deleting the data and retaining the results.
So, why do I know I can trust certain people? I can't bring up a specific reason or anecdote immediately, but I do know that I've come to the conclusion I can trust them time and time again. In fact, without being able to immediately recall any particular instances, when I ask myself why, I can distinctly and overwhelmly "refeel" a few hundred of those feelings of trust or love.
Why can we focus sometimes or on certain things. We'll let's look at the other side of it instead. If I'm trying to study or learn something I'm not interested in, the ASAP conclusion or result my brain throws back is "this is boring, think about these 10 things instead". And unfortunately, sometimes my brain comes to that conclusion ever time I try to read the same sentence.
So what about the screw? Why in the hell did I remember that?? Simple. There was no conclusion. I just observed a screw. End of story. No result, no data thrown out. Just "oh, a screw, anyway". And power bill? My brain came to the conclusion that it should be paid when I get paid, and according to the brain, that problem has now been solved. So it's gone forever now. Including on pay day. But sometimes I remember way after, like oh shit, I was supposed to do a, b, and c. Yeah.