ADHD is about having broken filters on your perception.
Normal people have a sort of mental secretary that takes the 99% of irrelevant crap that crosses their mind, and simply deletes it before they become consciously aware of it. As such, their mental workspace is like a huge clean whiteboard, ready to hold and organize useful information.
ADHD people… have no such luxury. Every single thing that comes in the front door gets written directly on the whiteboard in bold, underlined red letters, no matter what it is, and no matter what has to be erased in order for it to fit.