Speaking from personal experience, I've seen 4 cases which the family neglected,just because of "Na he's/she's fine,she/he doesn't need a doctor if they rest they'll be fine or something like
it's your imagination, she's having a bad day" and OF COURSE people screamed and told them LOOK at her/him do you Not see that somethings wrong with them? With all this I'm saying that even if in the current society it doesn't happen, in people of traditional views its not a big deal,so it is possible
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That's what I said: they can neglect but they notice that something is not really right.
I just notice that in many films, mangas and etc. they show people with mental ilness as some very good actors who can completely hide alarming symptoms. But in reality it isn't like that. Of course they can try to hide or manipulate others but especially close to them or more observant people realize that something is wrong with them. That's why they're ill because they don't completely control their behaviour. I just hope that author will disclose more this aunt and family situation in next chapters.
So a person who has ADHD is always going to have the urge to act out since people with a mental illness will always act a certain way? Got news for you. Most people with ADHD I know are very quiet. Weird.
If someone had ADHD, he behave in certain way otherwise he wouldn't be diagnosed, right. I also know people with ADHD and not every their behaviour I'd call completely normal. But why you even talk about ADHD because from what I could read his aunt can have borderline illness, maybe Munchausen syndrome. Maybe you though that we're talking about main male character?

His father is good guy but still pretty bad parent. And there is in this manhwa one thing which I really don't like but it's pretty often shown in others mangas, films and etc. If someone has serious psychological problems it's pretty impossible to people who live with them under one roof to not notice. I don't believe that parents of his mother would not notice something like that. They can neglect it but they have to notice that something is wrong with their daughter.