I think the huge mistake the writers did was writing such a charismatic and realistic SL but, most importantly, that first episode. Han Jipyung has basically the backstory of what looks like an amazing ML and then boom! just kidding! he's just here to suffer! I really do think that first episode set Nam Do san up because? of course the audience would love the SL more after a premise like that?? Also his relationship with the granma is basically the best thing ever.
The other problem I had with this kdrama is that there's a lot of weird af things that irl would have been a red flag or like ? Not Good and the writers just said yeah, whatever! like the fact that the ML is obsessed with a math test he cheated on when he was like. 13. or ??? the anger issues he has?? HELLO?? the FL too, she's cute and I think in the last episodes she finally grew out as a person but the fact that most of her story is centered about the two boys and jealousy... girl, that's not healthy at ALL...
I really really wish they would have let the characters grow as adults by themselves (most of the time they act like big ass children) and focus less on the love triangle because it really feels like everyone is doing what they're doing just to impress the person they like.
The cinematography and the OST are fire tho.