Firstly, I'm not sure if this is the right section, if it isn't please move it to it's right place!
I'm still new to dramas, so I don't have much experience, but after watching 13 Korean dramas, here is what pretty much all of them have in common:
Dead parents - At least 1 of the parents from one of the main characters is dead.
Tragic accident - One of the main characters was involved in a tragic accident when he/she was young, and was either injured/suffered a big trauma or at least one of the parents died.
Rich/Poor - One of the main characters is rich, the other one is poor (or becomes poor).
Old friend/cousin - The main character has a childhood friend or a cousin which he hates and/or is very competitive with.
Opposing parents - The parents of one of the main characters opposes to the relationship between the 2.
Love/Hate - Most of the main characters relationships start off with hate for each other.
I'm pretty sure there's more things they all have in common, but I can't think of any other right now... What else have you noticed? And is this something that literally all Korean dramas (well, not literally) have or am I just that lucky?