It does terrible things to your health, finances, employment and relationships.
My difficulty with basic chores almost cost me my marriage, and I spent north of 1000 nights in the last 5 years doing the dishes at 2am dead last before going to bed because that was the only circumstance under which I could get myself to do them.
I think most people misunderstand it greatly because their frame is "can't focus" but that's pretty nebulous. A better frame is "having a disastrously shitty batting average on choosing what to direct your attention towards or away from". The chronic understimulation leads to engaging predominantly in things that provide enough stimulation, which often aren't what you're supposed to be doing, and getting locked in that mode because anything else pales in comparison so switching away feels almost painful.
Best metaphor I've come up with to describe the difference is imagine you had to live your whole life with no shoes. Imagine all the surfaces you've ever had to walk across and how that would have been without shoes. You'd be fairly reluctant to make transitions between certain surfaces due to the discomfort. So the routes you take would change. Some routes would lead you to not wind up at your intended destination due to needing to walk on a comfortable enough path. You'd always take longer than other people to get places.
Also it's not a mental illness, it's a neurodevelopmental disorder.
