My uncle use to be a genius, and he got a brain aneurysm, the surgery saved his life, but he lost the capacity to retain information, he can't even read a book anymore. Was one of the great shocks of my life, he was my role model we use to talk about everything, read tons of books, and now he barely can keep up with a 10 year old kid.
Oh man, these were all such unfortunate incidents but the fact that the teacher and the uncle were, at the very least, able to live with their minds intact greatly past childhood and well into adulthood with well established identities, successful careers, able to meet and exceeded others expectations, is somewhat comforting, to me at least. Now when I think about it, I realize that Heejae couldn't even live through his entire childhood and lead his own future with what he used to posess for a fleeting amount of time. For someone who could've had a really bright future like the intelligent teacher and genius uncle at the very least, it's quite heartbreaking.
Losing your capacity to think, rationalize and connect concepts and notions together, and not having any control over it whatsoever since you can't change your innate brain structuring is probably the most despairing and hopeless thing ever.