Native Korean speaker here, born in the 70s and grew up in Seoul. We all learned a dozen short-long pairs at school (like 눈 nun being either eye or snow), and

Native Korean speaker here, born in the 70s and grew up in Seoul. We all learned a dozen short-long pairs at school (like 눈 nun being either eye or snow), and of course the education got all of us tricked into thinking that we're making these distinctions (if only we try hard enough). But looking at it objectively, I don't think a single person around me used vowel length distinction. If you have to "think" whether a word is long or short, that means the distinction is dead. No English speaker has to "think" whether fan or pan is the correct word. An actual sound distinction comes automatically for native speakers. Similarly, ㅐ/ㅔ ("ae"/"e") distinction was dead before I was born, but schools insisted that they're well and alive. Not sure what they're teaching these days.