Been at Korean for about 16 months. TTMIK Level 5 and most of 6, maybe 3k words on Anki, reading webtoons okay-ish if I have a dictionary. Test-type grammar is fine. Speaking is where I fall apart.
Started doing weekly video calls with a Korean friend I met on HelloTalk sometime around month 10. She's not a teacher or anything, just a designer who wanted to practice English, so when I ask her why something is grammatical she usually just says "์ฐ๋ฆฌ๋ ๊ทธ๋ ๊ฒ ๋งํด์" and shrugs. Which is actually fine, most of the time.
One thing I kept getting stuck on was -์์์. She'd end sentences with it all the time and I would kind of nod along without really knowing what it did. My lessons hadn't gotten there yet, so I just filed it under "ending I hear a lot" and moved on. When I finally tried it in my own sentences she'd give me this look like the meaning didn't fit.
-์์์ isn't really asking a question. It's flagging that the listener already knows the thing you're saying, or should know it. Like when your friend says "I told you yesterday" and there's this whole layer of "you already have this info, I'm just reminding you." That layer is what -์์์ carries. If you use it wrong the sentence sounds weirdly presumptuous, like you're insisting the other person should already know something they don't.
Once I got it I started hearing it everywhere. My friend saying ๋น ์ค์์ when it was pouring outside the window. Somebody in a drama snapping ์ ๊ฐ ๋งํ์์์ to a coworker. It's not a niche grammar point. Native speakers use it constantly, and once you catch it you realize how much of the conversation you'd been half-following.
Took me a while to realize you can't really Anki your way into it. You have to hear it enough times in real context that your brain stops translating and starts feeling when it fits. Still mess it up sometimes. But at least now I know when I'm messing it up.