well he was bullied a lot when he was younger and the stair incident definitely traumatized him. So he probably has social anxiety which makes it extremely difficult to just randomly talk to strangers
It depends on their personality/character. Like 2 guys wearing glasses doesn't always mean they both smart ( ̄∇ ̄") they just look smart. "don't judge a book by its cover" something like that (≧∀≦)
why Hirokawa cant speak properly?! Even the other lonely guy can... ¬¬