Someone who knows more feel free to correct me or expand on the context, but I believe that the characters in writing started out as Chinese and grew into Hangul later, so you'll sometimes see characters in time slip dramas struggle to read signs and things depending on when they jump to (there was a scene like that in Bon Appetit iirc). Wiki says that Hangul was introduced as a simplified alphabet with less characters than Chinese so more people could learn to read and write, so I think of it like Latin root words eventually turning into English phrases. By this time Hangul's been around for a hot minute tho, like 400 years