They know the rule but still cannot follow it in the moment

What to do right now

They can recite the rule. They understood it when you explained it. In the moment, the rule was in their prefrontal cortex and the impulse was in their amygdala. The amygdala fires faster. Knowing a rule and being able to follow it under pressure are two completely different cognitive functions. One is memory. The other is executive function under load. ADHD impairs the second one.

What your brain just did

Your body

They can state the rule perfectly. They violated it thirty seconds later. The gap between knowing and doing feels impossible.

Your brain

Rule knowledge is stored in declarative memory. Rule-following under pressure requires executive function: inhibition, working memory, and self-monitoring, all running simultaneously. ADHD impairs the execution system, not the knowledge system. They know. They cannot do, under load.

What this did

Move the rule from their memory to the environment. A sign on the wall, a visual cue at the point of action. External reminders bypass the internal system that fails under pressure.